Brn4/Pou3f4 is a POU-domain transcription factor expressed in the otic mesenchyme that is required for the normal development of the inner ear. In this report, we describe the isolation of an otic mesenchyme enhancer in the Brn4 gene. Subsequently, this enhancer was used to drive the expression of Cre recombinase in the otic mesenchyme of transgenic mice. When intercrossed with the ROSA reporter strain, R26R, ss-galactosidase expression is detected in several inner ear structures derived from otic mesenchyme, including the temporal bone, spiral ligament, spiral limbus, and mesenchyme underlying sensory epithelium of the utricle, saccule and semicircular canals. Thus, this Cre pedigree can induce conditional rearrangement of genes in the otic mesenchyme, and will serve as a powerful genetic tool to characterize the function of genes in the mesenchymal tissues of the inner ear.