MnAs initial growth on two different GaAs(001) reconstructed surfaces, namely As-rich c(4 x 4)alpha and Ga-rich 6 x 6, was investigated by scanning tunneling microscopy, and we surprisingly found that MnAs grows similarly on the both reconstructed surfaces despite large difference in their structures. MnAs layers grew two-dimensionally keeping zincblende-type crystalline structure until the completion of the first monolayer on both the reconstructed surfaces, and Ga atoms consisting of these reconstructed surfaces contributed to the growth, resulting in the anomalous evolution of nominal surface coverage. On the 6 x 6 substrate, the first monolayer was completed by only 0.1-0.2 ML of MnAs growth, while on the c(4 x 4)alpha 0.6-0.7 ML of MnAs growth is necessary to complete it. However, despite large difference in surface stoichiometry of the two surfaces, the surface structures during the growth closely resembled each other; i.e., both surfaces are essentially characterized by As-As dimers. (c) 2013 Elsevier B.V. All rights reserved.