Frogs and toads use acoustic signals for communication. The existence of several call types is recognized, but few studies have been made on them up to the present. The call repertoire of males and females of the Japanese treefrog, Hyla japonica was investigated in the field and laboratory. Six of the call types were confirmed: an advertisement call, an encounter call, a release call, a rain call, a distress call, and an amplexus call. The only call emitted by a female was the release call. Calls were categorized by observing behavior. Of the seven types of calls, only the advertisement call, which is used for mating, was analyzed in detail. The result showed that the temporal parameters (note duration and note repetition rate) were significantly correlated with air temperature; the dominant frequency was positively correlated with air temperature and negatively with snout-vent length; and that the frequency modulation was negatively correlated with the snout-vent length. Detailed acoustical and functional analyses of each type of calls would be expected in this species.