The use of microbial control strategies helps to control vibriosis, a disease that has long imposed a major threat to aquaculture industries. In this study, white shrimp (Litopenaeus vannamei) were fed a diet supplemented with Vibrio-antagonistic Bacillus pumilus D5 at concentration of 107 CFU/g for 8 weeks. No significant improvements of percent weight gain and feed efficiency were observed (p > 0.05). However, the numbers of Vibrio spp. in the tank water and hepatopancreas of the shrimp at day 10 were significantly lower in the experimental group (5.7 × 102 CFU/mL, 7.3 × 104 CFU/g) than in the control group (2.6 × 103 CFU/mL, 3.8 × 105 CFU/g) (p < 0.05). With regard to the immunity indicators, at week 8, the phenoloxidase activity and respiratory burst of white shrimp fed with the experimental diet (0.315, 0.566) were significantly higher than those of shrimp fed with the control diet (0.111, 0.380) (p < 0.05). The phenoloxidase activity of white shrimp after challenge with Vibrio parahaemolyticus was significantly higher in the experimental group (0.326) than in the control group (0.257) (p < 0.05). With regard to immune-related genes, the relative gene expression of Down syndrome cell adhesion molecule and prophenoloxidase before and after challenge with V. parahaemolyticus was significantly higher in white shrimp fed with the experimental diet (26.72, 4.83) than that in shrimp fed with the control diet (5.46, 1.60) (p < 0.05). The survival rate of white shrimp after challenge with V. parahaemolyticus was significantly higher in the experimental group (16.08%) than in the control group (4.76%) (p < 0.05). Overall, the results of this study indicated that B. pumilus D5 can decrease the numbers of Vibrio spp. in the tank water and hepatopancreas of white shrimp and enhance immune response and resistance to vibriosis infection in white shrimp.