The present investigation was undertaken to study the effect of dexamethasone (DEX) on immunity against Eumeria tenella (E. tenella) infection in chicken. Group 1 was kept as non-infected control. group 2 was infected with 10,000 sporulated oocysts of E. tenella per chick and is considered as infected group. The 3rd group: received 10,000 Eimeria oocysts per chick and was injected intramuscular with 0.1 mg dexamethasone every other day and is considered as infected dexamethasone group. The experimental chickens were challenged with 15,000 E. tenella oocysts. The results indicated the following findings: 1- Weight gain percent of infected chickens and livestock and infected treated with DEX was significantly lower than control. 2- The total oocysts output of E. tenella was Significantly higher in the group of infected chickens treated with DEX than control and infected groups. The lowest Eimeria oocysts count was noticed in the group of infected chickens.3- There was a significant decrease in weights of spleen, bursa Fabrics and thymus of infected chickens and infected chickens treated with dexamethasone. The lowest weights of spleen, bursa and thymus was recorded in infected induced chickens treated with DEX.