Mitf is a central regulator of pigment cell development that is essential for the normal development of the melanocyte and retinal pigment epithelium (RPE) lineages. To understand better the role of Mitf, we have used the Xenopus laevis experimental system to allow a rapid examination of the role of Mitf in vivo. Here, we report the function of XlMitfα-M on melanophore development and melanization compared with that of Slug that is expressed in neural crest cells. Overexpression of XlMitfα-M led to an increase in melanophores that was partly contributed by an increase in Slug-positive cells, indicating that XlMitfα-M is a key regulator of melanocyte/melanophore development and melanization. Moreover, overexpression of a dominant-negative form of XlMitfα led to a decrease in the number of melanophores and induced abnormal melanoblast migration. We also observed an induction of ectopic RPE and extended RPE by overexpression of XlMitfα-M and possible interactions between XlMitfα and several eye-related genes essential for normal eye development. Developmental Dynamics 234:523–534, 2005. © 2005 Wiley-Liss, Inc.