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Background: Noticing the importance of measuring physical activity in medical investigations, this study was conducted to analyze the validity and reliability of the researcher-made Physical Activity Questionnaire (AFPAQ) of Azad and Fesharaki, so as to achieve a suitable tool. Materials and Methods: In this cross-sectional study, the sample population all army men selected through two-stage cluster sampling according to Morgan samples table. After investigating content validity, confirmatory and explanatory factor analysis, Pearson correlation (using general health questionnaire (GHQ) and test-retest coefficient were used to examine construct and predictive validity, respectively. Data analysis was done using SPSS software version 15 and Amos version 16. Results: This study was done on 724 subjects including 54 (7.3%) women and 685 (92.7%) men. The CVR coefficient was 60% for this study. Also, explanatory factor analysis showed three factors, including physical activity at work, physical activity at leisure time, and exhaustion with 45% total variance and 71% Kaser-Meyer-Olkin Index. These factors were also confirmed by confirmatory factor analysis (AGFI=0.963, RMSEA=0.053). The reliability of the questionnaire was %40 and %70 using Cronbach's Alpha and test-re-test method, respectively. Conclusion: Since validity and reliability indexes of the questionnaire were reported desirable, AFPAQ can be considered a valid and reliable questionnaire for measuring physical activity