Here we report the structural and electronic properties of AunSn (n = 2-13) clusters by using pseudo-potential and LCAO-MO method. A comparison between the structures of Au-n and AunSn clusters reveals that while Au-n clusters favor planar isomers up to n = 13, AunSn clusters follow a different trend; 3D structure for n = 3 and 4, quasi planar in the size range n = 5-11, and again 3D isomers from n = 12 onwards. Enhanced contribution of Au p-orbital and significant charge transfer from Sn to the gold atoms is attributed for such interesting growth pattern of AunSn clusters. (C) 2012 Elsevier B.V. All rights reserved.