While the critical role of knowledge in motor (e.g., Allard, 1993) and physical education (PE) (e.g., Hare & Graber, 2000) performance is well-documented, insight is scant into the role that students' theories about what knowing is and how they come to know (Hofer & Pintrich, 1997) influence their achievement in PE. Links exist between such beliefs - that knowledge is simple (versus integrated) and certain (versus changing), that ability is fixed (rather than acquired), and that learning is quick not gradual - and performance in numerous academic domains. Related constructs studied in PE include misconceptions (Dodds et al., 2001) and having either fixed or incremental ability conceptions (e.g., Biddle et al., 2003). Calls for more domain-specific studies into relations between students' achievement and domain-specific beliefs about knowledge and learning (BKL) and ability conceptions form much of the rationale for this study. The descriptive study involves 315 ninth and tenth grade students in PE from schools in southwestern Ontario, Canada who reported their grade in PE and completed the Conceptions of the Nature of Athletic Ability II (CNAAQII revised for PE) Questionnaire (Biddle et al., 2003) and the 21-item (Likert style) BKL in PE Questionnaire (BKLPEQ) developed by the author using items with high factor loadings reported in previous educational research (e.g., Hofer, 2002). Exploratory factor analysis of the BKLPEQ extracted these five factors accounting for 45% of the variance: Quick Learning (QL), Simple-Integration of Knowledge (SIK), Mind-Body Beliefs (MBB), Simple-Utility for Knowledge (SUK), and Divine Attribution (DA). Internal consistency coefficients were moderate to high (.53 - .83). After partialing out overall academic achievement by using a structured multiple regression analysis, BKL strongly predicted PE grade: Increment in R2 was .06, F(5, 313) = 7.15, p < .001. The BKLPEQ factors SIK, MBB, SUK, and DA along with Entity-Goal Ability Conceptions (EGAC) from the CNAAQII each predicted achievement (p < .05). Correlation analysis revealed that students with less availing BKL (less sophisticated for in achievement in academic settings - see Muis, 2005 for a review) and higher EGAC had higher grades in PE. The results of this study affirm the role of BKL in PE and should serve as a springboard for initiating more research into how the content and instruction within PE might influence such beliefs. Discussion will include a proposal for why BKL in PE relates so differently to achievement in PE relative to achievement in more “academic” domains. Keyword(s): motor skills, physical education PK-12, research