Abstract: We had reported previously that when A. dims was fed on mice (Kunming strain) infected with Plasmodium yoelii yoelii (BY265 strain), the infection rate of salivary gland 3 and 4 days later was only 4.88%. In this paper we reported the increasing tendency of infection rates after several successive passages. The infection rate of salivary glands for the 3rd, 4th, 6th and 7th generations from the first blood passage was 31.7%, 70.0%, 6.9% and 30.0% respectively. Among 7 mice bitten by A, dims containing sporozoites of the 6th generation in their salivary glands two mice became infected. The number of sporozoites was over 2,000 in the salivary glands of A. dims when they were fed on mice with parasites of the 7th generation. The results suggested that there might be some adaptative selection of P. yoelii yoelii to A. dims.