Objective To study the effect of amikacin on aquaporin 4 (AQP4) expression in mice inner ear and reveal the possible mechanism of amikacin ototoxicity .Methods A total of 60 CBA/CaJ mice were randomly di-vided into experimental group and control group with 30 mice in each group .Experimental group mice were subcuta-neously injected with 450 mg/kg amikacin once a day for 2 weeks ,meanwhile control group mice were injected with normal saline .The expression of AQP4 were detected by immunohistochemistry .The changes of AQP4 protein and mRNA abundance were detected separately by Westen Blots and RT -PCR .Results AQP4 in mice inner ear mainly located in supported cells in Corti’s organ .AQP4 protein abundance in experimental group and control group were 0 .672 ± 0 .074 and 0 .479 ± 0 .108 ,mRNA abundance were 0 .701 ± 0 .107 and 0 .460 ± 0 .080 ,respectively .The a-bundance of AQP4 protein and mRNA in inner ear in amikacin -treated mice were significantly lower than those of in control group .Conclusion Amikacin may down -regulate AQP4 expression in mice inner ear .