PURPOSE: To obtain the title composition excellent in moldability and mechanical strengths and suitable for optical elements, by mixing an alkyl methacrylate (co)polymer of a specified weight-average MW with a copolymer of a monomer such as an alkyl methacrylate or N-phenylmaleimide with another monomer, having a specified weight-average MW.

CONSTITUTION: 50W100wt.% alkyl methacrylate monomer (a) of formula I (wherein R is a 1C or higher alkyl) and 50W0wt.% monomer (b) copolymerizable therewith [e.g., (α-methyl)styrene] are (co)polymerized to obtain a copolymer (A) of a weight-average MW of 105W3×105. 20W95wt.% component A is mixed with 80W5% copolymer (B) of a weight-average MW of 104W1.5×105, obtained by copolymerizing 30W95wt.% component (a) with 1W60wt.% monomer (c) of formula II (wherein X is at least one substituent which is any one of H, R and a halogen), e.g., N-phenylmaleimide, and 0W60wt.% monomer copolymerizable therewith (d) [e.g., (α-methyl)styrene].