Description: The present study was carried out to evaluate the dietary effects of Saccharomyces cerevisiae and Bacillus spore (B. licheniformis and B. latrospore) probiotic blend in guppy (Poecilia reticulata) larvae 30 days after the first feeding at ratios of 0.5*, 1 and 1.5%. Bacillus spores were used with the same density of 1x10 9 cfu/100 g in all treatments. There were no significant differences in larvae growth performance (P>0.05). A significant effect was observed when fish were challenged with Ichthyophtirius multifilus parasites (P<0.05). The highest survival percentage was observed in the group which received 1.5% yeast supplement and 1x10 9 cfu/100 g Bacillus spores. Also the highest mortality was related to group D1 which was fed a diet containing 1%I of Saccharomyces cerevisiae and Bacillus spore blend. This information indicates that the blend of Saccharomyces cerevisiae and Bacillus spore can act as immune stimulator to treat fish ectoparasites, Ichthyophtirius multifilus instead of chemical drugs.