Abstract: Four different cotton cultivars, which were proved to have different susceptibility to boron deficiency, were researched under soil culture condition The POD and SOD isozymes in cotton leaves were studied at their seedling stage both in boron deficient ( B,0 10mg B per kg soil) and boron sufficient (+B, 1 00mg B per kg soil) treatments It was found that B increased the number of POD and SOD isozymes in B ineffective varieties, but no change was found in B efficient varieties The increased isozymes must have good relationship with the capability of B deficient tolerance in different cotton cultivars, and differences were found between different growth stages (30 and 40 days) both in the two isozymes