Heat stress (HS) is one of the major economic problems facing the world's chicken industry. Besides decreased growth performance, HS reduces immune function in chickens. The principal part of the immunological function is the lymphatic organ. The spleen is a secondary lymphoid organ in birds. Sodium butyrate (SB) is the sodium salt of butyric acid and is suggested to be used to relieve heat stress. The current study aimed to evaluate the effect of sodium butyrate on the spleen in heat-stressed broilers. A total of 150 healthy broiler chicks (1 day old) were randomly divided into 4 groups: 1) control group fed on basal diet (BD) and normal temperature; 2) heat stress (HS) group (BD) and exposed to HS (34◦C for 8 h/day for 7 days starting from 29 days old); 3) low sodium butyrate group (BD + 0.5 g/kg SB every day and exposed to HS and 4) high sodium butyrate group (BD + 2 g/kg SB every day and exposed to HS. The spleen was harvested at the end of the experiments (36 days old). Our results revealed that HS caused severe damages, such as noticeable atrophy and loss of organization in the white pulp and hemorrhage in both white and red pulps. A low dose of SB supplementation showed full protection of the spleen tissue. However, the high dose might cause an adverse effect. In conclusion, SB especially low dose ameliorated the effect of heat stress. Therefore, we suggest using SB to face the heat stress in broilers, however with low doses.