The echolocation behavior of Pipistrellus abramus during exposure to artificial jamming sounds during flight was investigated. Echolocation pulses were recorded using a telemetry microphone mounted on the bats' backs, and their adaption based on acoustic characteristics of emitted pulses was assessed in terms of jamming-avoidance responses (JAR). In experiment 1, FM jamming sounds mimicking echolocation pulses of P. abramus were prepared. All bats showed significant increases in the terminal frequency (TF) by an average of 2.1–4.5 kHz when the TF of the jamming sounds was lower than the bats' own pulses. This frequency shift was not observed using jamming frequencies that overlapped with or were higher than the bats' own pulses. These findings suggest that JAR in P. abramusare sensitive to the TF of jamming pulses and that the bats' response pattern was dependent on the slight difference in stimulus frequency. In experiment 2, when bats were repeatedly exposed to a band-limited noise, the bats in flight more frequently emitted pulses during silent periods between jamming sounds. These results demonstrate that bats could rapidly adjust their vocalized frequency and emission timing to avoid frequency and temporal overlap with jamming sound even during flight. [Research supported by JSPS.]