The present inventions provide a method for commercially producing a 1,2-dihydropyridine-2-one compound represented by the following formula (III-a) wherein the ring A represents an optionally substituted 2-pyridyl group, the ring B represents an optionally substituted phenyl group, and the ring C represents an optionally substituted phenyl group. Further, the invention provides crystals of 3-(2-cyanophenyl)-5-(2-pyridyl)-1-phenyl-1,2-dihydropyridin-2-one and production processes therefor.