The equilibrium atomic structures of the Au3Pt3 cluster and NH3, H2S molecules are determined by Density Functional Theory calculations. The adsorption of NH3 and H2S molecules on Au3Pt3 cluster is then studied. The energy levels and the corresponding charge densities, adsorption energies, charge transfer and magnetization are calculated for different adsorption sites. We find that the adsorption generally modifies the structure of the Au3Pt3 cluster and the adsorbate. There exists strong interaction between Pt and N atoms. We observe that H2S dissociate at a specific site for the local density approximation (LDA) and one of the H atoms binds to Pt. In general, there is charge transfer from the molecules NH3 and H2S to Au3Pt3 cluster, for almost all adsorption sites. This makes the Au3Pt3 cluster semiconducting. (C) 2010 Elsevier B.V. All rights reserved.