Abstract: Immunoprophylaxis is widely acknowledged as a potential approach in the control of disease outbreaks in shrimp aquaculture. The present study evaluates the efficacy of dietary immunostimulants such as Fucus vesiculosus fucoidan (FCD), Eucheuma cottonii κ-carrageenan (CAR), heat-killed Vibrio harveyi cells (VHK), Vibrio harveyi lipopolysaccharide (VLP) and yeast β-glucan (BGN) in enhancing the immunological response and the resistance of juvenile Penaeus monodon against Vibrio harveyi infection. Experimental diets were incorporated with the test immunostimulants at 2.0 g kg-1 and a two-week feeding trial was conducted. Following the feeding trial, the experimental shrimp were challenged with pathogenic Vibrio harveyi through intramuscular injection and immunological responses were measured. Results showed significant enhancement of shrimp survival after Vibrio harveyi infection in the FCD (82.2%), BGN (84.4%) and VLP (84.4%) dietary treatments as compared to the control (51.1%), CAR (55.6%) and VHK (42.2%) treatments. The high survival against Vibrio harveyi infection in these treatments is associated with the prominent enhancement of hemocyte phagocytosis (VLP: 118.63±4.42; BGN: 120.01±0.60; FCD: 127.41±1.52) and serum antibacterial activities (VLP: 9.02±0.21; BGN: 9.19±0.012; FCD: 9.61±0.31) as compared to the hemocyte phagocytosis (CAR: 103.10±0.59; VHK: 108.01±2.02; Control: 79.170±1.06) and serum antibacterial activities(CAR: 7.61±0.01; VHK: 7.90±0.16; Control: 5.01±0.09) of the control and the other treatments. These results suggest that dietary supplementation of VLP, BGN and FCD at a dose of 2.0 g kg-1 can be used to boost the immunological response and enhance the resistance of P. monodon against Vibrio harveyi infection.