Lactic acid bacteria, Lactobacillus spp. (LAB) are a group of probiotics which are often practiced in aquaculture to enhance growth of aquatic species. In this study, we tried to investigate the effect of powdered LAB added diets on microflora of intestines and on growth of orange-spotted grouper, Epinephelus coioides. After 28 days of feeding, the total numbers of vibrios and LAB were counted by plate colony count and the growth was measured. The results showed that the numbers of LAB of intestines increased with dosage. The number of vibrios reduced owing to the inhibitory effect of LAB. The groupers that were fed with 2.0% and 1.0% of powdered LAB added grew faster than others. In addition, LAB did not affect water quality. Base on the study, it was suggested that a suitable amount of 1.0% LAB added diets could be used in grouper culture to have better growth.