A styrene resin composition comprising a crosslinked styrene resin and uniformly dispersed therein an uncrosslinked resin capable of being extracted with an organic solvent, the amount of the uncrosslinked resin being from 3 to 50% by weight based on the total amount of the composition; and a method of producing a molding of a styrene resin composition, which method comprises the step of subjecting to cast polymerization a liquid mixture comprising: (a) a styrene monomer in an amount of 30% by weight or more based on the total amount of the ingredients (a), (b), and (c); (b) a monofunctional monomer having one radical-polymerizable double bond in the molecule, in an amount less than 70% by weight based on the total amount of the ingredients (a), (b), and (c); (c) a polyfunctional monomer having at least two radical-polymerizable double bonds in the molecule, in an amount of from 0.01 to 40% by weight based on the total amount of the ingredients (a), (b), and (c); (d) a resin component soluble in a mixture of the ingredients (a), (b), and (c), in an amount of from 3 to 100 parts by weight per 100 parts by weight of the total amount of the ingredients (a), (b), and (c); and (e) a free-radical polymerization initiator in an amount of from 0.001 to 5 parts by weight per 100 parts by weight of the total amount of the ingredients (a), (b), (c), and (d).