Abstract: This invention provides an agent for inhibiting production of hepatitis C virus with notable anti-HCV activity and without side-effects. The agent comprises a proanthocyanidin polymer composition illustrated in the following the general formula (1), wherein R1 is hydrogen or hydroxyl, R2 is hydroxyl, R3 is hydrogen when R1 is either hydrogen or hydroxyl, but R3 is possibly hydroxyl when R1 is either hydrogen or hydroxyl to the extent that both R1 and R3 being hydroxyl is at most 40 percents in the proanthocyanidin polymer composition said units of flavan-3-ol being bonded each other in any one of three patterns as follows; (i) a bond between carbon at the position 4 and carbon at the position 8, (ii) a bond between carbon at the position 4 and carbon at the position 6, (iii) a bond between carbon at the position 4 and carbon at the position 8, and between carbon, at the position 2 and oxygen at the position 7.