Chironomid midges breeding in Lake Biwa were collected by the authors and their collaborators during the period from April 1985 to June 1986 mainly using three different methods; 1) The collection of adults resting or swarming on the lake shore with nets or sucking tubes. 2) The collection of larvae together with bottom sediments and water weeds and their rearing in the laboratory to obtain emerging male adults with which the identification of species was made. 3) The collection of adults with a light trap operated once a week on the shore of the lake. As a result, a total of 71 chironomid species were collected and identified in and around the lake. Of the collected species, 47 belonged to the subfamily Chironominae, 18 to Orthocladinae, 1 to Diamesinae, and 5 to Tanypodinea. The collection included 6 new species and 5 species new to Japan, and morphological and taxonomical accounts have been presented for these species. The seasonal trends of the emergence of two giant midges, Chironomus plumosus and Tokunagayusurika akamusi, from the lake were observed by means of the light trap samples. Ch. plumosus, a cosmopolitan lake midge, seemd [i.e. seemed] to appear three time a year, in early April, June and September, while T. akamusi, a species indigenous to East Asia, appeared only once in November. The collection contained a number of taxonomically interesting species. For example, Biwatendipes motoharui Tokunaga (1965) was collected in large numbers in April resting on the lake shore, and proved to have very noteworthy morphological characters more or less intermediate between the tribes Chironomini and Tanytarsini of the subfamily Chironominae. All the six new species described in this paper, Camptochironomus biwaprimus, Paratanytarsus biwatertius, Tanytarsus kirai, T. biwatrifurcatus, Cricotopus biwannulatus, and Eukiefferiella biwaquarta, showed morphological characteristics not found in previously recorded chironomid species.