The present study aimed to explain the role of additives in alleviation of the negative effect of heat stress on differential leucocytes count, heterophil / lymphocytic ratio with especial studies on the microbial count of duodenum, jejunum, ileum and caecum. A total of 270 day-old (Ross308) broiler chickens randomly divided into 6 groups, which were kept under elevated temperature (34-36◦C) and feed diet containing 1% Nigella Sativa (G2) or a mixture of sodium bicarbonate and potassium chloride (0.3% KCL+ 0.5% NaHCO3) (G3) or 2% coriander seed (G4) or 0.03% Acetylsalicylic acid (aspirin) (G5) or 250 mg of Ascorbic acid (Vitamin C) (G6) for 6 weeks. The previous parameters were recorded after slaughtering to take microbial sample and collecting blood parameters. The results explained that, there was a significant increase lymphocyte percentage in case of G2, G3, G4, G5 and G6. while, there was significant decreases in Heterophil percentage, heterophil/lymphocyte ratio (H/L), eosinophils percentage, monocytes percentage, jejunum total colony count and caecum total colony in case of (G2, G3, G4, G5), (G6, G2, G3, G4, G5), (G6, G3), (G5; G2), (G3; G2) and (G2, G4) respectively in compared with control group (P<0.05). It could be concluded that black seed and coriander seed have a positive effect on heat stress broiler diet.