To evaluate the vector efficiency of Anopheles sinensis in transmitting vivax malaria in the northern part of Gyonggi-do, South Korea, daily survival and feeding host preferences were studied during the period of June-October 1999. Ovaries of unfed and freshly fed An. sinensis females were dissected and parity or nulliparity were observed. The parous rates were 75.2% in July, 56.5% in August, 78.5% in September, and 60.0% in October at Gusan-dong, Goyang-si, Gyonggi-do. The average probability of daily survival was 0.890. To determine the host feeding patterns of An. sinensis, outdoor-resting bloodfed mosquitoes were collected, and the sources of the blood meals were analyzed by enzyme-linked immunosorbent assay, using 6 different animal immunoglobulin G antibodies. Out of 305 blood meals tested, 0.7% were positive from humans, 89.8% from bovines, 3.3% from swine, 0.7% from dogs, 1.6% from chickens, and 0.7% from bovines and swine mixed. No blood meals were positive from mice. Though the vector efficiency of An. sinensis was poor because of a low human blood index and a moderate rate of daily survival, vectorial capacity would be high because of high density of the population.