Abstract: A monomer comprising methyl methacrylate either alone or in combination with another acrylic or methacrylic ester monomer is partially polymerized to prepare a syrup, to which an initiator including a peroxide having a 10-hour half-life temperature of 50.degree. to 58.degree. C. and 2,2'-azobisisobutyronitrile are added. The resulting syrup, after being poured into a mold, is initially polymerized in a first step at a temperature of 75.degree. to 90.degree. C. for a period of 5 to 15 minutes, then further polymerized in a second step at a temperature 3.degree. to 12.degree. C. lower than the temperature of the first step polymerization until a conversion of monomer to polymer of 80 to 95% is attained. The polymerization product which is now in the form of a sheet is then heat-treated at a temperature of 95.degree. to 140.degree. C. to obtain a methacrylic resin sheet.