Ecological studies were conducted on marine chironomids in south-western Japan. A total of 20 species was collected. For vertical distribution, only a few species was distributed only at high or middle intertidal zone while many species were distributed only at low zone. For substrate preference, some species were collected only on rocks or in mud while many species were collected only in seaweeds. For geographical distribution, a few species was collected only in the southwestern islands or in the oceanic coast in the Japanese main islands. In contrast, some species were collected in the Seto Inland Sea and the oceanic coast in the main islands, in the oceanic coast in the main islands and the southwestern islands, or in all areas. For seasonal emergence, Dicrotendipes enteromorphae was collected only in summer and autumn, and Semiocladius endocladiae was collected in all seasons. Other species were collected only in autumn and winter, or only in winter and spring. These results suggest that many chironomid species with a variety of lifestyles dwell in intertidal zones and have some important roles in the ecosystems.