To obtain a resin composition for flame retardant molding materials having sufficient flame retardancy and workability.

This resin composition for flame retardant molding materials comprises a radically polymerizable resin containing a phosphoric acid ester (meth)acrylate and aluminum hydroxide. The phosphorous atom content in the radically polymerizable resin is 0.7-10 wt.% based on the whole amount of the radically polymerizable resin. The phosphoric acid ester (meth)acrylate is at least one species selected from a group comprising phosphoric acid monoester (meth)acrylate, phosphoric acid diester (meth)acrylate and phosphoric acid triester (meth)acrylate and the relation among the molar ratio (M1) of phosphoric acid monoester (meth)acrylate, the molar ratio (M2) of phosphoric acid diester (meth)acrylate and the molar ratio (M3) of phosphoric acid triester (meth)acrylate is expressed by the following equations, 1.5≤[(M1)×1+(M2)×2+(M3)×3]≤3 and (M1)+(M2)+(M3)=1.