A method for the manufacture of a polybutadiene-modified unsaturated polyester, comprising the steps of: (I) reacting (A) an .alpha.,.beta.-unsaturated dicarboxylic acid or anhydride with (B) at least one compound selected from the group consisting of (i) air-drying allyl compounds, (ii) animal and vegetable oils or derivatives thereof and (iii) dicyclopentadiene or derivatives thereof at a (B)/(A) molar ratio within the range of from 0.8 to 1.2, and (II) reacting the resultant reaction product with (C) at least one compound selected from the group consisting of .alpha.,.omega.-polybutadiene glycol and .alpha.,.omega.-hydrogenated polybutadiene glycol. A polybutadiene-modified unsaturated polyester comprising said polybutadiene-modified unsaturated polyester and a polymerizable monomer possessing at least one double bond.