In this work, a novel efficient one-step method for preparation of acrylated soybean oil (ASO) was introduced. ASO was obtained by reacting soybean oil (SO) and acrylic acid (AA) directly under the catalysis of BF3·Et2O. Effects of reaction stoichiometry and reaction time on the conversion of the double bonds of SO were studied. 1H NMR analysis indicated that the number of acrylate groups could reach 3.09 per triglyceride molecule or the conversion of the double bonds was up to 75.7%. Copolymerization of the ASO and styrene was demonstrated, and the flexural and dynamic mechanical properties of the resulting polymers were evaluated.