This is the first report on the nocturnal flight activity of the phlebotomine sandflies in the field by trap collection in Mukusu, Masinga, the kala-azar (visceral leishmaniasis in humans) area in Kenya. A total of 514 sandflies were collected with three different types of traps (sticky traps, CDC light traps and a goat-baited trap), and seven species of two genera (Sergentomyia and Phlebotomus) were identified. The number of Sergentomyia bedfordi Newstead individuals captured was the largest among these seven species. This suggests that S. bedfordi is the most common among the seven species in Mukusu. The result of the sticky trap collection suggests that the wild sandflies are nocturnally active, with the highest flight activity level soon after sunset, at least for S. bedfordi. The proportion of females collected was extremely high both in the sticky and light trap collections. It is suggested that this is due to site tenaciousness or weaker dispersal urge of males. Phlebotomus martini Parrot, S. bedfordi and S. schwetzi Adler, Theodor and Parrot were collected in the goat-baited trap. Examination of the physiological conditions of a total of 495 females collected showed that almost all females were unfed and nulliparous. This suggests that younger females show stronger nocturnal flight activity.