Abstract: When they are flying,Great evening bat (Ia io) produces short FM echolocation calls including three harmonics,of which the first one and the second one are stronger.As they fly,the first harmonic is modulated from 49.0 to 18.3 kHz,the second one is modulated from 80.0 to 35.6 kHz,and the third one from 87.2 to 56.7 kHz.The average duration of the calls is 3.7 ms.It was predicted t hat Great evening bat (Ia io) captures big insects in the open area among foliages according to the sound characteristic analysis of echolocation calls and the analysis comparing with the echolocation calls of other bats that perch in the same cave.