Mosquitoes are transmit many dangerous disease such as malaria, yellow fever and dengue fever. So far, chemical insecticides such as DEET have been mainly used to control mosquitoes, but there are many side effects. This study used ultrasonic sounds as an alternative to chemical insecticides. We found that Culex pipiens, which are common in Korea, exhibit avoidance behavior in a specific ultrasonic frequency. Through electrophysiological recording, we have inferred that avoidance behavior is caused by different from each other mechanisms depending on the ultrasonic frequency. Using immunohistochemical staining, we analyzed the expression pattern of auditory related genes in the chordotonal organ. Quantitative real time-PCR was used to compare the expression levels of auditory related gene depending on the time of exposure to ultrasonic sounds.