The purpose of this study investigate the effect of anaerobic threshold training of endurance in elementary school swimmers. for this purpose 12 elementary school swimmers were put to 8-weeks session of anaerobic threshold training based on critical velocity. The data were abalyzed by paired t- test with p<.05 as the level of significance using SPSS statical package ver. 12.00 The result obtained are as follows: 1. Though exercise career is short,, anaerobic threshold training based on critical velocity is an index of the improvement of cardiopulmonary endurance training by maintaining 3~4 mM/l lactate level 2. The endurance tarining set mode(Table 10) for elementary school swimmer is next table based on blood lactate level and critical velocity for elementary school swimmers with variety of exercise career. 3. There are statistically signifficance relationship between anaerobic threshold training and endurance foctor . This result mean that treatment of anaerobic threshold training influence the improvement of aerobic endurance in elementary school swimmers.