Abstract: The laying hens of 250 day old were divided into high antibody group(HA)or low antibody group (LA) acood-ing to the fifth day' s plasma-antibody liter to sheep red blood cells(SRBC) after primary intravenous immunization. Then studied the effects of high ambient temperature on the immunability of HA chicks and LA chicks. The results as follows:(1)In normal conditions there were no significant difference between LA chicks and HA chicks in lymphocyte transformation (P>0. 05);but LA chicks had more white blood cells than HA chicks (P<0. 01)and the value of heterophil lymphocyte(H/L)of LA chicks was also higher than HA chicks (P<0. 05).(2)Acute heat stress (22 ℃~30@ ,24h)significantly inhibited lymphocyte transformation of HA chicks but it had no influences on LA chicks. Chronic heat stress (35℃ ,5 days old)significantly inhibited both HA chiek' s and LA chick' s lymphocyte transformation (P<0. 05 and P<0. 01 .respectively)(3)Chronic heat stress had no influences on total white blood cells of HA chicks;but increased significantly the values of H/L (P<0. 01). On the contrary,chronic heat stress decreased the total of white blood cells of LA chicks, and had no influence on the value of H/L.