Introduction: Many studies have investigated the relationshipbetween motivation and educational outcomes. The present studywas conducted to determine whether the students’ motivation inShiraz University of Medical Sciences (SUMS) decreases duringeducational years.Methods: 770 students in SUMS were selected by multi-stage stratifiedrandom sampling from each field and entrance year. The firstquestionnaire contained 57 questions on the effect of economic, social,educational, geographical and personality factors on the students’motivation. The second one was based on 50 incomplete sentences.The validity and reliability of these questionnaires were approvedby the experts and Cronbach’s Alpha coefficients (85% and 90%,respectively). In this cross-sectional study, ANOVA, t-test and Chisquaretests were applied for data analysis at the 0.05 significance level.Results: Six factors with the most effect on academic motivationwere “family attitudes”, “getting good jobs in future”, “respect forthemselves”, “ the ability to learn”, “believing their role in victory anddefeat” and “the tendency toward optimism about themselves”. Inaddition, comparing professional doctorate and basic sciences’ resultsrevealed no significant relationship between academic motivationand educational years (F=0.819, p=0.397). But comparing field byfield showed that Dentistry and Hospital Management and MedicalInformation (HMMI) had a significant decrease in motivation scoreby increase in educational years (F=3.991, p=0.015).Conclusion: Achievement motivation level in SUMS studentswas higher than average and did not decrease during educationalyears. Also, the results showed that personal, social andeducational related factors affected motivation level more thaneconomic and environmental factors.