Abstract: A medical resin composition is produced by mixing a powder of a polymer (A) comprising repeating units having an ester group and a liquid of a vinyl ester monomer (B) having 6 or more carbon atoms to increase a viscosity and, according to demand, further performing a polymerization reaction. The thus produced resin composition inhibits leaching of irritative substances, reduces any adverse effects on the human body by endocrine disruptors, etc. and can be prepared with high operational efficiency. The resin composition is suitably used as a dental resin composition such as a tissue conditioner, a functional impression material, a lining material, a denture base material or a mouth piece material.