Members of the microRNA (miRNA) 183 family (miR-183, miR-96, and miR-182) are expressed abundantly in specific sensory cell types in the eye, nose, and inner ear. In the inner ear, expression is robust in the mechanosensory hair cells and weak in the associated statoacoustic ganglion (SAG) neurons; both cell types can share a common lineage during development. Recently, dominant-progressive hearing loss in humans and mice was linked to mutations in the seed region of miR-96, with associated defects in both development and maintenance of hair cells in the mutant mice. To understand how the entire triplet functions in the development of mechanosensory hair cells and neurons of the inner ear, we manipulated the levels of these miRNAs in zebrafish embryos using synthesized miRNAs and antisense morpholino oligonucleotides (MOs). Overexpression of miR-96 or miR-182 induces duplicated otocysts, ectopic or expanded sensory patches, and extra hair cells, whereas morphogenesis of the SAG is adversely affected to different degrees. In contrast, knockdown of miR-183, miR-96, and miR-182 causes reduced numbers of hair cells in the inner ear, smaller SAGs, defects in semicircular canals, and abnormal neuromasts on the posterior lateral line. However, the prosensory region of the posterior macula, where the number of hair cells is reduced by approximately 50%, is not significantly impaired. Our findings suggest both distinct and common roles for the three miRNAs in cell-fate determination in the inner ear, and these principles might apply to development of other sensory organs.