Crossing experiments among 6 strains of Anopheles sinensis from Koniya, Kanoya, Karuizawa, Yomogita, Yakumo and Engaru were done by induced copulation; the number of eggs per female, the hatchability, and the fertility of the F1 hybrids were investigated. The hybrid males between the Engaru strain and either the Kanoya or the Yakumo strain showed complete sterility. The hybrid females showed low fertility. Restoration of fertility of the hybrid females and males from those crosses were found in BC2. No mature spermatozoa were observed in the testes of the hybrid males from the cross of the Engaru strain with the Kanoya strain. Therefore, the Engaru strain of An. sinensis is considered genetically to be a full species. The relationship between the Engaru strain of An. sinensis was discussed.