To generate temporally‐controlled targeted somatic mutations selectively and efficiently in smooth muscles, we have established a transgenic SMA‐Cre‐ER^T2 mouse line in which the expression of the Tamoxifen‐dependent Cre‐ER^T2 recombinase is under the control of a large genomic DNA segment of the mouse smooth muscle α actin (SMA) gene, contained in a Bacterial artificial chromosome (Bac). In this transgenic mouse line, Cre‐ER^T2‐mediated recombination of LoxP‐flanked target DNA is strictly Tamoxifen‐dependent, and efficient in both vascular and visceral smooth muscle cells. Moreover, with the exception of few cardiomyocytes, LoxP‐flanked DNA excision is restricted to smooth muscle cells. Thus, SMA‐Cre‐ER^T2 mice should be of great value to analyze gene function in smooth muscles, and to establish new animal models of human smooth muscle disorders. genesis 47:14–18, 2009. © 2008 Wiley‐Liss, Inc.