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The antagonistic action of the gut microflora of the tiger shrimp (Penaeus monodon) from three different farms (A, B and C) was tested against four bacterial shrimp/fish pathogens viz., Aeromonas hydrophila, A. sobria, Vibrio vulnificus and V. fischeri using the double agar overlay method. The total bacterial load of gut microflora ranged from 106 -108 cfu.g-1. The bacterial composition of shrimp gut predominantly consisted of Vibrio sp. (30-52%) followed by Bacillus sp., Pseudomonas sp., Photobacterium sp., Plesiomonas sp. Of the 185 isolates tested, 26.27% showed antagonistic action against fish/shrimp pathogens. The gut microflora, Pseudomonas sp. and Photobacterium sp. of farm A; and Bacillus sp. of farm C inhibited the fish pathogen, A. sobria, while Vibrio sp. and Corynebacterium sp. of farm C inhibited A. hydrophila. Only a single strain of Vibrio sp. (C2) from farm C was found to show antagonistic action against the shrimp pathogen, V. vulnificus. The intestinal gut microflora of shrimp shall therefore be evolved as putative probiotic bacteria to counteract disease problems.