A renal function-ameliorating agent and a serum creatinine-lowering agent, each comprising as an active ingredient a culture of a bacterium belonging to the genus Bacillus, are disclosed. The bacterium belonging to the genus Bacillus is preferably Bacillus subtilis, and more preferably Bacillus subtilis C-3102 (FERM BP-1096). The renal function-ameliorating agent and the serum creatinine-lowering agent are useful for treating and preventing diseases such as arteriosclerosis.