Abstract: In order to study the effect of weak noise on the sound signal extraction of mouse (Mus musculus Km) inferior collicular (IC) neurons from environments,we examined the changes in frequency tuning curves (FTCs) of 32 neurons induced by a weak noise relative to 5 dB below minimum threshold of tone (reMT-5 dB) under free field stimulation conditions.The results were as follows:1) There were three types of variations in FTCs,sharpened (34.4%),broadened (18.8%),and unaffected (46.9%),nevertheless,only the alteration of sharpened FTCs was statistically different.2) Sharpness of frequency tuning induced by a reMT-5 dB noise was very strong.Q10 and Q30 of FTCs were increased by (34.42±17.04)% (P=0.026,n=11) and (46.34±22.88)% (P=0.009,n=7).3) The changes of inverseslopes (Iss,kHz/dB) between high (Ishigh) and low (Islow) limbs of FTCs were dissymmetry.The Ishigh of FTCs decreased markedly (P=0.046,n=7),however,there was little change (P=0.947,n=7) in Islow.Our data revealed for the first time that the weak noise could sharpen frequency tuning and increase the sensitivity on the high frequency of sound signal in IC neurons of mouse.