The aerobic bacterial flora of larval swimming crabs (Zoea-I to Crab-I) cultured in three hatcheries were investigated in relation to the microflora of rearing pond water and diets. The external and internal bacterial counts of the crab on ZoBell's 2216 e agar ranged from 102 to 104 and 101 to 104 CFU/animal, respectively. The number of the bacterial counts increased as the developmental stages progressed. In respect of constitution, Vibrio and Pseudomonas predominated both in external and internal bacterial flora.The total bacterial counts for rearing pond water, live diets (rotifer and brine shrimp) and minced/artificial foods ranged 104105, 106108, and 103105 CFU/ml or g, respectively. The bacterial flora of rearing pond water and live diets consisted of mainly Vibrio and Pseudomonas, while from the minced food and artificial food only Pseudomonas was predominantly isolated.