Balance involves a complex of dynamic interactions of vestibular, visual, and somatosensory information. The aim of the present study was to evaluaterelationship between knee and trunk extensor muscles strength with balance. 297 male students of guidance level of Guilan Province were selected through cluster random sampling. Star excursion balance test and a dynamometer were used to measure balance and strength of knee and trunk extensor muscles respectively. Pearson correlation coefficient and multivariate regression were used to test the hypothesis of the study. α level was set 0.05. The results of the study showed a significant correlation between three groups of muscles strength with balance. By regarding the results of the study, it seems that knee, hip and trunk extensor muscles strength have basic role in balance.