Natural rubber serum powder (NRSP) was found to have a marked growth-stimulating effect on Bifidobacterium bifidum, one of the prevalent species of bifidobacteria in the human intestine, which is widely employed in the food industry. Addition of NRSP to the medium enhanced metabolite production and yield. NRSP stimulated growth in a similar manner to casein, including the exertion of a synergistic effect. However, the effects of the concentrations of casein and NRSP on the growth of B. bifidum were different. Ammonium sulfate, one of the major components of NRSP, aided the growth of the test strain as a nitrogen source, and other active ingredients of NRSP are also likely to exercise additive nutritional effects.