BMP signaling plays pleiotropic roles in various tissues. Transgenic mouse lines that overexpress BMP signaling in a tissue‐specific manner would be beneficial; however, production of each tissue‐specific transgenic mouse line is labor‐intensive. Here, using a Cre‐loxP system, we generated a conditionally overexpressing mouse line for BMP signaling through the type I receptor ALK2 (alternatively known as AVCRI, ActRI, or ActRIA). By mating this line with Cre‐expression mouse lines, Cre‐mediated recombination removes an intervening floxed lacZ expression cassette and thereby permits the expression of a constitutively active form of Alk2 (caAlk2) driven by a ubiquitous promoter, CAG. Tissue specificity of Cre recombination was monitored by a bicistronically expressed EGFP following Alk2 cDNA. Increased BMP signaling was confirmed by ectopic phosphorylation of SMAD1/5/8 in the areas where Cre recombination had occurred. The conditional overexpression system described here provides versatility in investigating gene functions in a tissue‐specific manner without having to generate independent tissue‐specific transgenic lines. genesis 44:159–167, 2006. Published 2006 Wiley‐Liss, Inc.