The present study deals with the role of probiotics in ornamental fish platy Xiphophorus maculates. Two distinct colonies were isolated from the intestine of Platy through serial dilution technique and pour plate method. Two distinct colonies were isolated from the intestine of Platy through serial dilution technique and pour plate method. The isolated colony was identified by using biochemical tests and identified as Bacillus subtilis. The identified microbe Bacillus subtilis was mass multiplied by using nutrient broth. Five different feeds having different concentration of Bacillus subtilis such as Ex. Feed I (Control), Ex. Feed II (10¹ cells), Ex. Feed III (10² cells), Ex. Feed IV (10³ cells) and Ex. Feed V ( 10⁴ cells) were prepared by using fish meal, ground nut oil cake, wheat flour, tapioca flour, fish oil, sunflower oil, supplevite- mix, sodium chloride and sodium benzoate. Role of microbes on feed utilization parameters such as feed consumption, feed conversion efficiency, feed conversion ratio, growth, percentage growth, relative growth rate, assimilation, metabolism, net and growth efficiency of Platy were studied for a period of 30 days. Feed consumption was higher in Ex. Feed V containing 10⁴ cells of Bacillus subtilis. The growths, percentage growth, relative growth rate, gross and net growth efficiency was also higher in Ex. Feed V containing higher cells of Bacillus subtilis. Assimilation and metabolism were also higher in Ex. Feed V. From the results, it is inferred that the Ex. Feed V was suitable for the growth of platy.