1. In the sympatric congeneric tits (Paridae and Aegithalidae), some comparative studies of the methods in the use of bills and the structure of the among the bill species were made and the ecological separation, as related with the spaces for each species were discussed. The vegetation of the studied area is a mixed deciduous woods in central Japan, as detailed by T. Nakamura (1970, 1975).2. The species features in the morphological characters shown by body length, wing length, tail length, tarsus length, toe length, bill length, bill width and bill depth are as follows:Long-tailed Tit (Aegithalos caudatus) has a smaller body but a longer tail, wing, and tarsus in relative length than Parus species. The bill of Long-tailed Tit is shorter and has a more curved shape than Parus species.In Parus, the relative length of tail is smaller than that of the Long-tailed Tit and the relative length of toes is greater than that of Long-tailed Tit. The shape of the bill in Parus is more similar to the simple cone than that of Long-tailed Tit. Great Tit (Parus major) has larger toes and their bill is not specialized as compared with other three species of Parus. Coal Tit (Parus ater) has a smaller body but has a relatively long wing than other Parus species. The shape of the bill of Coal Tit is thin and pointed. Willow Tit (Parus montanus) has the toes with large claws, and the length of the hind and the midde toes is almost the same. The bill of Willow Tit has a larger relative depth (ratio of depth to width or length) than the other three species of Parus. Varried Tit (Parus varius) has a larger body length and a pointed bill. The shape of the bill of this species is flattened at the tip like a flat chisel.3. The species features as represented the methods of using the bill in attacking the preys and picking seeds are as follows:Long-tailed Tit often takes the hunging posture on a twig of larch and deciduous trees, and quick picking and pecking are the most simple methods of using the bill. However, Parus species have more varied methods in the use of the bill and more varied attacking sites than Long-tailed Tit. Especially, it is characteristic of Parus species that they have methods of processing by their bill on the sites or objects where they suppose available food existed and they often hammer them and remove the food. Great Tit removes a piece of bark on the branch or the trunk or a fallen leaf on the ground. Coal Tits destroy the buds or a lump of dead leaves clung to twigs by bitting or thrusting by their bill. Willow Tit digs up dead parts in trees, often while hunging under the branches or twigs. Varried Tit holds seeds, acorns, insect galls or other ball like matters on perch by their toes and crushes them pecking by the bill.4. The methods in the use of the bill well correspond with the morphological characteristics of the bill in each species. Due to the large differences in the use of the bill, in the structure of the bill and in the sites for attacking preys between Long-tailed Tit and Parus species, their coexistence will be possible in various locations in Japan. I think that the ecological differences between Long-tailed Tit and Parus species are larger than such interspecific differences within genus Parus, such as the differences in the shape of bills. These congeneric interspecific differences may not allow the coexistance of species within Parus completely but only uncompletely. Therefore, the species compositions of Parus in sympatric ranges vary from site to site.5. The methods in the use of bills well correspond with the micro-structure in a microhabitas.