Abstarct: The purpose of the current study was the effect of the lower extremities pre-cooling on the 50 and 100 meter breast-stroke swimming time at the collegiate swimmers.this study is quasi experimental and applied. for this reason, 12 collegiate swimmers (22.08 years; 180 cm; 75.08 kg) Were selected Purposefully to participate in the study. Then, Subjects Participated in two separate sessions (exercise with and without precooling) with 4 days rest periods in this study. The exercise protocol was 6 min warm up with 60% VO2max and breast-stroke swim 50 and 100 meter. In one session that exercise done with Precooling Subjects were immersed in cold water up to waist high for 8 minutes. The main variables of research (50 and 100 meter swim time) measured by chronometer. Moreover, heart rate, core body temperature, blood lactate and Borg Rating of Perceived Exertion (RPE) Scale were measured during and after exercise. mean record of 50 and 100 meters in pre-cooling group (respectively 74 and 126 seconds) was less than mean non- precooling group (82 and 128 seconds), which did not show a significant difference (p<0/05). Also, mean (RPE) Scale in the precooling group (1/42) was less than mean non- precooling group (2/67) which show a significant difference between two group (p<0/05). Conclusion: The results suggest that, however precooling leg muscle can not improved 50 and 100 meter record in college swimmers, but it can cause to reduce exertion.