To explore the effect of porcine intestinal antimicrobial peptides (AMP) on hematology indexes and oxygen free radicals of broiler chicken under heat stress condition.Methods3010-day-old Arbor Acre broiler chickens were randomly allocated to three groups with 10birds per group. The groups were control group (normal room temperature), heat stress group (simulate summer high temperature), and AMP treated group (2mg per bird) under heat stress condition. The chickens were treated with high temperature for 10days, 8hours per day. Serum was collected after ten days. Results The results showed that whole blood viscosity, plasma viscosity, and packed cell volume of AMP treated group under heat stress condition had significant difference compared to heat stress group(P＜0.01); TP, GLO, GLU, ALT, AST and ALP of AMP treated group were significantly higher than those of heat stress group; TC,TG, UREA, LDL and HDL of AMP treated group were significantly lower than those of heat stress group. Comparison between AMP treated group and heat stress group revealed significantly increase of SOD and GSH-Px (P＜0.01), and decrease of MDA (P＜0.01). ConclusionIn conclusion, AMP could modulate blood components and flowing deformation, improve humoral immunity, balance oxygen free radicals to resist heat stress. Therefore, AMP has the potential as immunomodulator in broiler production.