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Shrimp farming is one profitable sector of aquaculture and the Pacific white shrimp (Litopenaeus vannamei) is the most cultivated species worldwide. Nutrition is considered as one of the greatest challenges in shrimp farming due to its dependence on fishmeal (FM) as an ingredient in the feed. The main goal of the present work was to analyse if the substitution of FM by yellow mealworm (Tenebrio molitor) meal (TM) influences digestive enzyme expression, haemolymph parameters or the intestinal microbiota of shrimp juveniles. Shrimps (average initial weight 4.42±0.02 g) were fed five experimental diets where FM protein was gradually substituted by TM protein (0, 25, 50, 75, and 100%). The shrimps were fed four times per day with an amount equivalent to approximately 6% of their biomass for 42 days. The total haemocyte count, protein concentration and prophenoloxidase activity in the haemolymph were not significantly altered (P>0.05) when FM was substituted by TM. However, the agglutinating activity of shrimp serum determined against dog erythrocytes was higher in the shrimp group fed 25% TM. The absolute and specific activities of trypsin, chymotrypsin, lipase, α-amylase and the patterns of proteolytic activities were not affected by the dietary treatments. The shrimp gut bacterial microbiota profile was similar with the genera Pseudoalteromonas, Rubritalea, Ruegeria, Tenacibaculum, and Vibrio detected. These results show that TM is viable alternative for the replacement of FM, without any deleterious effects on expression of key digestive enzymes, gut microbiota or the immune system of the Pacific white shrimp.