Abstract: Two varieties of maize(Zea mays L.,cultivars Dahuang and Qing No.3) were used in the study.The results showed that a heat shock(HS) treatment significantly increased the survival percentage of two variety seedlings at heat stress,confirming heat-shock increased heat tolerance of maize seedlings.More-over,the maize seedlings through heat pretreatment,retained relativelyhigher activity of glutathine reductase(GR,EC 1.6.4.2) than the seedlings without heat-shock pretreatment.In the profiles glutathine reductase isozyme in the seedlings after heat-shock-pretreatment appeared a new band as compared with the seedlings without heat-shock pretreatment.Changes in isozyme profiles of GR had been different during heat stress.These indicated thathigher activity of GR and changes in isozyme profiles of GR were related to heat tolerance of maize seedlings.