How can Reasoning Skills be Improved? -An experimental study of the effects of Reasoning Skills Curriculum on reasoning skills development for students in postsecondary vocational education programs. Reasoning skills could be synthesized and defined as cognitive processes focusing on purposeful and self- regulatory interpretation, analysis, inference, evaluation, and judgment. The main objectives of reasoning skills lie on rational deliberation to evidence, context, conceptualizations, methods, and criteria. Reasoning skills have been identified to construct under the mechanism: First of all, reasoning is motivated with the induction by stimuli. Second, reasoning is a goal-oriented process. Third, reasoning functions based on information, knowledge, and experience. Fourth, reasoning operates mainly by way of language. Fifth, reasoning is driven by intelligence or reasoning skills. Sixth, reasoning is also under the influence of personal thinking dispositions, habits, personal positions, motives, and other social/cultural factors. Finally, meta-cognition emphasizes individuals' self-monitoring and regulation of the thinking process. The improvement of Reasoning Skills has been highly valued as a major educational goal for long. These skills are also increasingly needed in current society filled with various information resources and multifarious senses of value. However, the reasoning education seems not to succeed as expected due to the lack of effective instructional strategies and systematic curricula. Related research mostly addressed the fundamental theories; but the reasoning skills curricula and practical assessment were severely limited. Therefore, this study was conducted to continue a series of reasoning skills development research and identify the effects of this innovative curriculum on the improvement of these competencies for students in postsecondary vocational education programs. The sample participating in this study, consisted of 23 students, was selected in a vocation-oriented university located in the central Taiwan, R.O.C.. During the one- semester experimental period, nineteen reasoning sub- skills were taught as the major contents using contemporary social issues in order for participants to integrate reasoning skills with daily life affairs. A group discussion model was the main teaching strategy combining with instructor's lecturing. Qualitative research method, using teacher's portfolio strategy, was employed to continuously collect data and analyze the development of students' reasoning skills during the whole period. This study finally indicated that this instruction successfully assisted students to improve their reasoning skills from the stage of dual thinking style to responsible knowing. Qualitative research method was identified as an appropriate strategy for reasoning skills assessment to envision the developmental process of students' reasoning skills while receiving some instruction. Some suggestions concerning effective teaching strategies and reasoning skills assessment were also provided on the basis of findings and conclusions for the improvement of reasoning education as follows: (1) Reasoning Skills can assist students to envision the entire development and effects of the professional knowledge, and facilitate students' transferable abilities for their professional skills. (2) The curriculum contents and implementation of all courses need to foster students' understanding of knowledge, analyses of theoretical background, synthetic evaluation competency, and high order cognitive competencies. (3) The social culture and campus environment significantly nurture the growth of students reasoning skills. A series of campus symposia for public discussions on academic arguments and social issues assist students to envision the functions of reasoning skills and create beneficial campus facilitating reasoning skills development. (4) There is another effective approach to create a discussion area through university websites and/or community internet for further interaction among campus members. The internet, therefore, can be utilized in universities for students to reach the social issues and understand multifarious viewpoints. (5) Teacher's portfolio, incorporating the characteristics of both qualitative and quantitative research methods, assists instructors to deeply envision the effects of reasoning skills intervention on the students' reasoning skills development. (6) Future researches are suggested to explore professional courses in order to understand the validity of Reasoning skills intervention and the improvement of teaching strategies for Reasoning Skills. (7) Some consequent questions concerning with the structure of these nineteen sub-skills and the interactive relation among them are also proposed for profound understanding of nature and organization of the reasoning skills. Keywords: Reasoning Skills, Postsecondary Vocational Education, Reasoning Assessment