PURPOSE: To obtain a composition containing tannins and water soluble vegetable fiber, capable of suppressing production of harmful substances which enteric bacterium produce, excellent in effect for proliferating enteric usable bacteria and effect for suppressing proliferation of enteric harmful bacteria and useful for promotion of health.

CONSTITUTION: The composition contains (A) one or two or more tannins selected a group from (+)-(gallo)catechin, (+)-gallocatechin gallate, (-)- epicatechin (gallate), (-)-epigallocatechin (gallate), free theaflavin, theaflavin monogallate A, theaflavin monogallate B and theaflavin digallate and (B) a water-soluble vegetable fiber (e.g. enzymatically decomposed material of guar gum) such as a water soluble vegetable fiber whose chain length of straight chain is distributed in the range of 30-200 units in a ratio of ≥80% and the mixed weight ratio of the component A and the component B is 1/30-1/6. Furthermore, the doses of the component A and the component B are 0.001-0.03g/kg weight and 0.08-0.50g/kg weight, respectively.