耳石（学名：otolith；οτο-，oto-，耳朵 + λιθος，lithos，石头）是脊椎动物内耳内的碳酸钙结晶（霰石）组织，位于位于内耳前庭系统的椭圆囊及球状囊。椭圆囊与水平直线加速度有关，球状囊与垂直加速度有关，均属于静态平衡。在耳石膜中的耳石晶体附着在胶质覆膜上，比周围组织重，因此在定向加速度时会发生位移，导致毛细胞的纤毛束转向，产生感觉信号。大部份椭圆囊产生的信号是由眼球运动所触发，而大部份球状囊所产生的信号则是反应出控制人体姿势的肌肉运动。

硬骨鱼类的耳石,又名鱼首石，在鱼类形态学研究尤为重要，主要是藉其物种辨识能力，应用于鱼类物种的族群管理、鱼类掠食者的食性分析，以及重建古鱼类等各项功能。这是由于耳石形态的专一性。

An otolith (οτο-, oto-, ear + λιθος, lithos, a stone), also called statoconium or otoconium or statolith, is a structure in the saccule or utricle of the inner ear, specifically in the vestibular labyrinth of vertebrates. They have been identified in both extinct and extant vertebrates. Counting the annual growth rings on the otoliths is a common technique in estimating the age of fish. The saccule and utricle, in turn, together make the otolith organs. They are sensitive to gravity and linear acceleration. Because of their orientation in the head, the utricle is sensitive to a change in horizontal movement, and the saccule gives information about vertical acceleration (such as when in an elevator).