Megastigmus grandiosus n. sp., reared from pine cones from Mexico, is described and illustrated.The genus Megastigmus Dahlbom contains many species occurring throughout the world. They are generally phytophagous on seeds of pine cones and entomophagous on insects associated with plant galls.A new species, Megastigmus grandiosus, was reared from the cones of Pinus montezumae Lamb., P. rudis Endl., P. ayacahuite Ehremb., and P. hartwegii Lindl. (Pinaceae: Gymnospermae). The specimens were taken at Calpulalpam, Tlaxcala, Mexico, and sent to me by Dr A. Hedlin, Pacific Forest Research Centre, Canadian Forestry Service, Victoria, B.C. I am describing this new species here so that it may be included in the publication by the North American Forestry Commission, FAO, on conè and seed insects of North America.