Pacific white shrimp Litopenaeus vannamei (Boone, 1931) is an important economical shrimp species worldwide, especially in the Middle East region, and farming activities of this species have been largely affected by diseases, mostly viral and bacterial diseases. Scientists have started to use prebiotics for bolstering the immune status of the animal. This study aimed to investigate the influence of Immunogen® on growth, digestive enzyme activity and immune related gene expression of Litopenaeus vannamei post-larvae. All post-larvae were acclimated to the laboratory condition for 14 days. Upon acclimation, shrimps were fed on different levels of Immunogen® (0, 0.5, 1 and 1.5 g kg−1) for 60 days. No significant differences were detected in weight gain, specific growth rate (SGR) and food conversion ratio (FCR) in shrimp post-larvae in which fed with different levels of Immunogen® and control diet. The results showed that digestive enzymes activity including protease and lipase increased with different amounts of Immunogen® in the shrimp diet. Protease activity increased with 1.5 g kg−1 Immunogen® after 60 days and lipase activity increased with 1 and 1.5 g kg−1 Immunogen® after 30 and 60 days of the trial respectively (P < 0.05), while amylase activity did not change in response to different levels of Immunogen® (P > 0.05). The expression of immune related genes including, prophenoloxidase, crustin and g-type lysozyme increased with diet 1.5 g kg−1 Immunogen® (P < 0.05) while expression of penaeidin gene increased only with experimental diet 1 g kg−1 of Immunogen®. These results indicated that increase in digestive enzymes activity and expression of immune related genes could modulate the Immunogen® in the innate immune system in L. vannamei in this study.