Pressure-volume (P-V) behavior and radiation-induced polymerization of methyl and n-butyl acrylic esters (MA and BA, respectively) were studied up to 7000 kg/cm2at 20°C. The P-V isotherms broke at 1900 and 1200 kg/cm2for MA and BA, respectively. The P-V isotherm for MA was not smooth in the pressure range between 3500 and 4000 kg/cm2. The polymerization behavior varied with change in the P-V behavior; the polymerization rates were maximum at 1800 kg/cm for MA and 1000 kg/cm2for BA, and then minimum at 1900 kg/cm2for MA and 1100 kg/cm2for BA. The polymerization rates increased again above the pressures giving the minimum rates up to about 3000 kg/cm2. Above 3000 kg/cm2the pressure dependence of the rates decreased up to 4000 and 4500 kg/cm2for MA and BA, respectively. Above these pressures, the pressure dependence of polymerization rates increased again. The P-V isotherms of as-polymerized polymer-monomer coexistence systems showed characteristic behavior near the polymerization pressure. From a comparison of these polymerizations and P-V behavior with those of methacrylic esters, we propose that acrylic esters align at high pressure and that freedom of rotation of ester group plays an important role in the mode of pressure-induced alignment of monomer molecules.