Four feeding trials were conducted to evaluate the effects of dietary probiotics as antibiotic replacers in Japanese eel, Anguilla japonica; Nile tilapia, Oreochromis niloticus; Whiteleg shrimp, Litopenaeus vannamei; and Olive flounder, paralichthys olivaceus. In the first experiment, growth performance, non-specific immune responses, immune-related gene expression and cumulative survival rate of Japanese eel fed Bacillus subtilis WB60 (0.5× 10 7 CFU/g) with mannanoligosaccharide (5g/kg)-BSM diet were significantly higher than those of fish fed control (CON) diet. However, there were no significant differences among fish fed BSM and oxytetracycline (OTC) diet. In the second experiment, growth performances, non-specific immune responses, cumulative survival rate of Nile tilapia fed B. subtilis at 1 × 108 (CFU/g)-BS and Lactococcus lactis at 1 × 108 (CFU/g)-LL diets were significantly higher than those of fish fed CON diet. However, there were no significant differences among fish fed BS, LL and OTC diets. Immune-related gene expression and enzyme activity of BS and LL diets were significantly higher than those of fish fed CON and OTC diets. In the third experiment, growth performance, non-specific immune responses and cumulative survival rate of whiteleg shrimp fed B. subtilis at 1 × 108 (CFU/g)-BS and L. lactis at 1 × 108 (CFU/g)-LL diets were significantly higher than those of shrimp fed CON diet. However, there were no significant differences among fish fed BS, LL and OTC diets. Immune-related gene expression and histology of shrimp fed the probiotic diets were significantly improved compared to those of shrimp fed CON and OTC diets. In the fourth experiment, growth performance, non-specific immune responses, immune-related gene expression, cumulative survival rate and enzyme activity of olive flounder fed B. subtilis at 1 x 10 8 CFU/g (BS), L. lactis at 1 × 10 8 CFU/g (LL), E. faecium at 1 x 107 CFU/g (EF7) and E. faecium at 1 x 10 8 CFU/g (EF8) were significantly higher than those of fish fed CON diet. However, there were no significant differences among fish fed BS, LL, EF7, EF8 and OTC diets. These results indicated that BSM in Japanese eel; BS and LL in Nile tilapia and Whiteleg Shrimp; BS, EF7 and EF8 in Olive flounder could be ideal synbiotics or probiotics to improve growth performance, immune responses, enzyme activity, disease resistance and gene expression, and to replace antibiotics in those for major aquaculture species in the esst Asian countries Korea, Japan, China, etc.