The purpose of study was to investigate the influence of isokinetic knee joint muscle strength on duty form in the fire fighters. 28 men who aged 30-40 years were measured by isokinetic knee joint muscle strength testing(Cybex 6000 dynamometer system). Subjects were divided into the 2 groups that were indoor duty group and outdoor duty group. Statistical analysis was performed using analysis of variance t-test. In results, peak torque and average power of indoor duty group was showed significantly lower than that of outdoor duty group. At comparison of right and left knee joint, isokinetic strength, isokinetic power and isokinetic endurance of right knee joint was showed significantly higher then that of left knee joint, but in 60 degree per second, left knee joint was showed higher then that of right knee joint. Result from this investigation show greater presonal training and fire quell a riot, emergency rescue activity was increased knee joint muscle strength. Therefore, physical fitness and health maintance programs for fire fighters have been developed, implemented, and proven to reduce morbidity and mortality and financial expenditures.