In order to determine the monomer reactivity ratio in copolymerization of acrolein, the copolymerization of acrolein with styrene, methyl methacrylate and vinyl acetate respectively was studied. The Q and e value of acrolein in each copolymerization were also calculated from those of monomer reactivity ratios, but the calculated values were slightly different from each other. The Q and e of acrolein for the system of acrolein-styrene copolymerization were Q = O.64 and e = O.62 respectively. Relations among the Q and e value, the composition and structure of copolymers and the mean sequence length in copolymerization were also discussed for acrolein copolymers.