Objectives : Cheonggukjang(natto) is known to have anti-hyperlipidemic action in our previous study. This study was designed to investigate the safety of Prototype-cheonggukjang (PC, Herbal-natto). Methods : We investigated the effects of PC on changes in body weights, food uptake, water uptake, levels of AST/ALT, levels of BUN/creatinine and electrolytes in serum from normal mice. PC is made by cheonggukjang added Codonopsis Lanceolata, Houttuynia cordata and Lentinus edodes in indicated concetrations. Results : In this experiment, PC group showed equal levels of body weights, urine volume compared to non-treated control group. Oral administration of PC did not affect food and water uptake too. Levels of AST/ALT, which are markers of liver function, were not changed by administration of PC. In addition, levels of BUN/creatinine, which are markers of renal function, were not affected by PC too. Finally electrolytes in serum were not affected by PC. Conclusions : These results imply that oral administration of PC is safe in the framework of liver and renal function, and electrolytes in serum.