Abstract: In order to obtain the suitable conditions for cowpea chemical mutation，taking cowpea cultivar‘Tianchang 9’and‘Yin-jiang-wang’as experimental material and setting 3 kinds of EMS concentration with 3 treatment time，the effect of seed germination，seedling growth，and major biochemical indexes of seedling were studied. The results showed that the germination energy and germination percentage of cowpea seeds were decreased，whereas the electrical conductivity of their leaching liquid，SOD activities and soluble protein content of seedling were increased with EMS treatment. While seeds were treated with 0. 3%，0. 5% and 0. 9% EMS solution，the induction time of half lethal dose were 4. 41，3. 63，3. 59 h in cultivar‘Tianchang 9’，and 2. 04，1. 03，0. 79 h in cultiva‘r Yin-jiang-wang’，respectively.

Key words: cowpea, EMS, electrical conductivity, germination rate, SOD, protein, LD₅₀