The present experiment was designed to study effects of broiler strain and dietary level of enzyme cocktail (PhytaBex® Plus), on productive performance, some blood plasma parameters and lymphoid organs. A total of 270 one-day old broiler chicks (135 Avian chicks and 135 Cobb chicks) were distributed over six experimental groups according to a (2 х 3) factorial design. There were three different experimental diets presented to chicks within each strain as; T1: fed basal diet (BD); T2: BD + PhytaBex® Plus (100 g/ ton) and T3: fed BD + PhytaBex® Plus (200 g/ ton). Live body weight (LBW) and daily weight gain (DWG) during starter phase showed that chicks of Cobb strain recorded significantly higher LBW and DWG compared to chicks of Avian strain, whereas, birds fed T2 or T3 diets had heavier LBW and recorded higher DWG compared to those fed T1 diet. Strain, enzyme level and their interactions, had no significant effects on final LBW or DWG during grower phase. Values of daily feed intake (DFI) during starter phase showed that chicks of Cobb strain recorded significantly higher DFI compared to chicks of Avian strain, while, birds fed T2 or T3 diets consumed more feed than those fed T1 diet. Additionally, DFI during grower phase presented no significant differences between strains, whereas enzyme level had significantly decreased DFI of birds fed T1 diet compared to birds fed T2 or T3 diets. Values of feed conversion ratio (FCR) during starter or grower periods, indicated no significant differences between strains, enzyme levels or their interactions. Enzyme level had no significant effect on all of blood plasma parameters, except for plasma cholesterol, while strain had a significant effect on most of blood plasma parameters except for plasma albumin and cholesterol. Relative weights of lymphoid organs were not significantly affected by strain, dietary enzyme level or their interactions. Finally, it could be suggested that addition of enzyme cocktail PhytaBex® Plus in dietsof Cobb or Avian broiler strains, had some favorable effects on productive performance, with no harmful effects on bird's immunity or blood plasma traits.