Description: Action research has been regarded as a means to promote teachers' continuing professional development. Characteristically, action research reports written by teachers take a form of a narrative. In this paper, based on an empirical study and a review on the methodological discussion on narrative research, the problem of validity of action research narratives is discussed. As a conclusion, some principles for assessing the quality of narrative research reports are proposed. According to some methodologists, action research is narrative in nature, regardless of whether or not the researcher recognises this. The teachers' narratives of developing their work focus on individual experiences, report these experiences chronologically, and present a temporal sequence of events. The narrative form is typical not only for teacher-driven action research but a more general trend in the field of educational and social research. Along with the narrative turn in social sciences, various kinds of experimental narrative expressions have become popular. Simultaneously, the quality of research has become a more and more intricate issue. In our presentation, we are not willing to accept an extremely relativistic "postmodern" stand within narrative research. So as to avoid relativism, we need some conceptual tools to grasp the problem of quality of narratives, but tools different from the traditional concepts of validity and reliability, which harbour markedly positivistic connotations. In this paper, we apply five principles for judging the quality of action research from a narrative point of view. Firstly, the narrative acknowledges the past course of events that have shaped the present practices (1. the principle of historical continuity). Secondly, we emphasize the reflexive nature of a good research narrative (2. the principle of reflexivity). Thirdly, we propose that a good research narrative takes various views into account (3. the principle of dialectics). Often the quality of action research is evaluated through its pragmatic results. Thus, we need a pragmatic view which asks whether the project actually produces some useable practices which, in one way or another, can be regarded as useful (4. the principle of workability). Furthermore, we agree with Aristotle, who claims that a good narrative involves a balance between "logos", "ethos" and "pathos". Therefore, we would add some more emphasis on "ethos" and "pathos" , following Michael Quinn Patton's ideas of artistic and evocative criteria of assessing research quality (5. the principle of evocativeness). In our presentation, we illustrate these five principles through some empirical examples based on a data of an action research project which aims at developing pedagogical methods to integrate environmental education and health education in the 5th grade in a Finnish primary school. Methodology: A philosophical analysis, related to an empirical study, on the epistemological assumptions beyond action research and narrative research. Conclusions: Principles for validating action research narratives. Promoting discussion on the validation of teacher research.