This paper reports on a research done to study learning styles and their roles in the academic achievement of the students of Payame Noor University (PNU), Ardebli center, Iran. 184 students (90 male and 94 female students) in the fourth semester are chosen as our sample using Cocran's formula and random sampling. The questionnaire memletics is used to collect data about learning styles. Reliability of this questionnaire is calculated as a=0.81 using Cronbach's alpha. Total average of students' scores in four semesters is taken as a criterion for academic achievement. Findings show that most of male students use verbal and solitary learning styles. Most of female student use aural and verbal learning styles. The academic achievement of female students is more than the academic achievement of male students. Among the students of Payame Noor University, those who use visual learning style have the greatest achievement. Students with social, aural, verbal, and solitary learning styles are in the following ranks respectively. Students with logical and physical learning styles have the least academic achievement.