An antiviral preparation comprising as an active ingredient, a phorbol derivative of formula 1: wherein is R1 —(CH2)aX(CH2)bCH3, —(CH2)cX(CH2)dYCH3, —CO(CH2)eCH3 or —(CH2)fCH3 R2 is —CO(CH2)nCH3, R3, R4 and R5 are hydrogen atom, or an aliphatic or aromatic carboxylic acid residue, X and Y are O or S, and each of a-f and n is a number, and having a specific safety index S.I.=CC50/EC50 of 10 or more wherein EC50 means a concentration at which HIV-1 induced cytopathogenic effect (CPE) in MT-4 cell is inhibited by 50%, and CC50 means a concentration at which survival of MT-4 cell in a cell proliferation test is reduced by 50%. These preparations are particularly effective for human immuno-deficiency virus (HIV).