An antiviral preparation comprising as an active ingredient, a phorbol derivative of formula 1: ##STR00001## wherein is R.sub.1 is --(CH.sub.2).sub.aX(CH.sub.2).sub.bCH.sub.3, --(CH.sub.2).sub.cX(CH.sub.2).sub.dYCH.sub.3, --CO(CH.sub.2).sub.eCH.sub.3 or --(CH.sub.2).sub.fCH.sub.3 R.sub.2 is --CO(CH.sub.2).sub.nCH.sub.3, R.sub.3, R.sub.4 and R.sub.5 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.=CC.sub.50/EC.sub.50 of 10 or more wherein EC.sub.50 means a concentration at which HIV-1 induced cytopathogenic effect (CPE) in MT-4 cell is inhibited by 50%, and CC.sub.50 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).