A method to control the copolymer composition in suspension polymerizations of monomers with different polarity was studied: the copolymerization of a styrene‐type monomer having THF moiety (1) with styrene (feed ratio 1 : 1) was carried out at 85 °C using benzoyl peroxide (BPO) in a suspension system consisting of water and monochlorobenzene. The copolymerization was greatly affected by a mixture ratio of suspension system, and when the H2O : PhCl ratio was 7 : 1 (v/v), 1 and St were consumed almost at the same rate, which suggested the formation of a random copolymer with uniform composition. The copolymer was proven to have an identical structure as expected, and a composition ratio of 1 : 1 by 1H NMR analysis and elemental analysis. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 453–458, 2001