Cochlea of the inner ear is essential for hearing. Cochlear sensory epithelium consists of hair cells, supporting cells, and tectorial membrane (TM), an extracellular matrix lying over the apical surface of the epithelium. Acoustic stimuli vibrate the epithelium and deflect hair bundle of the hair cells. This event opens mechanosensitive channels on hair bundle, which induces cation entry and excites the hair cells. TM is crucial for vibration of hair bundle. Although sensory differentiation and maturation occurs rapidly around birth, the regulatory factors remain obscure. Here, by comparing bulk RNA transcripts of the epithelium between neonatal (1 day old) and adult (3 month old) mice, we found that Smoc2 (SPARC-related modular calcium binding 2) encoding a matricellular protein is highly expressed during development. In neonatal mouse cochlea, Smoc2 mRNA was detected in hair cells as well as a subpopulation of supporting cells, which produces TM components. Immunolabeling revealed that, besides plasma membranes of these cell types, Smoc2 protein could be also localized to TM. Because Smoc2 can interact with BMP signaling that is required for hair cell formation (Ohyama et al., JN 2010), this matricellular protein may regulate the development of not only TM but also sensory epithelium.