The aim of this study was to investigate the effects of using citric acid and multi carbohydrase enzymes on phytase efficacy on the humoral immunity of broiler chickens fed diets with nutritionally marginal calcium and nonphytate phosphorous (Ca-nPP). A total of 320 one-day-old male broiler chickens were randomly assigned to 8 treatment groups, with 4 replicates per treatment and 10 chicks per replicate in a completely randomized design. Eight dietary treatments containing, T1: adequate level of Ca-nPP as positive control diet (CTL+), T2: reduced levels of Ca-nPP as negative control (CTL−), T3: negative control diet + 1000 unit/kg phytase, T4: negative control diet + 1 % citric acid, T5: negative control diet + multi carbohydrase enzymes, T6: negative control diet + 1000 unit/kg phytase and 1 % citric acid, T7: negative control diet + 1000 unit/kg phytase and multi carbohydrase enzymes and T8: negative control diet + 1000 unit/kg phytase +1 % citric acid + multi carbohydrase enzymes. Blood samples were taken from each bird and the titers of maternal antibody against Newcastle disease virus (NDV) and avian influenza virus (AIV) were measured by haemagglutination-inhibition (HI) test. Addition of phytase to the diet increased significantly (P<0.05) antibody production against NDV and AVI as compared to birds fed CTL− diet in T2. In conclusion, the inclusion of citric acid and multi carbohydrase enzymes to the diet improved the effectiveness of phytase on antibody production against NDV and AVI in broiler chickens.