The present invention provides a copolymer excellent in terms of heat resistance, flowability, mechanical property, appearance, low water-absorbing property, and moldability. Also provided is a process for producing a copolymer, the obtained copolymer being excellent in terms of heat resistance, flowability, mechanical property, appearance, low water-absorbing property, and moldability. The copolymer according to the present invention contains 80 mol% or more methyl (meth)acrylate units (A), and has a Vicat softening temperature of 115DEG C or higher, a saturation water absorption at 60DEG C of 4 mass% or less, and a yellow index of 1 or less. The process for producing a copolymer comprises: suspension-polymerizing a monomer mixture comprising 80 mol% or more methyl (meth)acrylate (a) and0.7-7 mol% (meth)acrylic acid (b) to obtain a precursor; and melt-kneading the obtained precursor with an extruder to obtain a copolymer which comprises 80 mol% or more methyl (meth)acrylate units (A), 0.45-7 mol% (meth)acrylic acid units (B), and 0.001-0.25 mol% glutaric anhydride units (C).