The present invention relates to an isolated Bacillus sp. strain having probiotic activity. More particularly, the present invention relates to an isolated Bacillus sp. 2-4 (KCCM11107P) strain having probiotic activity. Since the strain of the present invention functions as probiotics by having an antibacterial activity against various fish pathogenic bacteria, as well as secreting helpful enzymes such as protease, amylase, cellulose, and lipase to help the digestion and absorption of the feed, the strain of the present invention can be helpfully used as a feed additive for fish and crustaceans.