Production of a bifidogenic growth stimulator (BGS) by propionibacterial strains was investigated using lactic acid as a carbon source. The maximum concentration (1.9 mg/L) of BGS was obtained in the mono-cultivation of Propionibacterium shermanii using 20 g/L of lactic acid. The co-cultivation, in which lactose was gradually converted only to lactic acid by a homo-fermentative lactic acid bacterium and subsequently the lactic acid was used as a carbon source for BGS production by P. shermanii, resulted in the successful BGS production. The BGS concentration obtained in the co-cultivations P. shermanii and Lactobacillus casei or P. shermanii and Lactobacillus bulgaricus seas 1.8 or 6.4 mg/L, respectively.