PURPOSE: To provide a resin composition having low odor and low heat-generation tendency, resistant to cracking, and having high mechanical strength, by adding dimethallyl o-phthalate, etc. to a radically polymerizable resin containing radically polymerizable unsaturated group at a specific ratio.

CONSTITUTION: The objective composition is produced by mixing (A) 100pts.wt. of a radically polymerizable resin having 0.5W6 radically polymerizable unsaturated groups per molecular weight of 1,000 [e.g. a vinyl ester resin composed mainly of (meth)acrylic acid-modified epoxy resin, etc.] with (B) preferably 30W 150pts.wt. of dimethallyl o-phthalate and/or dimethallyl isophthalate, by conventional method.

EFFECT: The working environment and the moldability can be improved.