A novel exopolysaccharide (EPS) was isolated from a probiotic bacterium, Bacillus coagulans RK-02. In vitro proliferation studies showed that the EPS stimulated both the splenocytes and thymocytes. The nitric oxide induction of the EPS was tested on peritoneal macrophages. It was observed that the EPS induced macrophages to produce NO. The immunostimulatory studies of the EPS was also tested in vivo. The results indicated that the EPS stimulated splenocytes, thymocytes and induced the macrophages to produce NO significantly. The toxicity of the EPS was evaluated in both the in vitro and in vivo studies. Toxicity studies of the EPS clearly indicated that the purified EPS was non toxic.