In this paper, we investigate the adsorption properties of single Pt and O atoms, and PtO, Pt2O, and PtO2 clusters on hexagonal AlN monolayer as well as several substitutions in AlN structure. We employ density functional theory to study electronic structure and charge transfers by considering nonmagnetic and ferromagnetic states. PtO and Pt2O adsorbed AlN system has ferromagnetic ground state with 2.00 mu(B) magnetic moment, while PtO2, Pt, and O adsorption lead to nonmagnetic structures. Pt adsorbed AlN system has the lowest adsorption energy with -3.175 eV indicating the most stable structure energetically. Oxygen atom largely disrupts the AlN layer due to strong N-O repulsion caused by high electronegativities of N and O atoms. The substitution of AlN monolayer with Pt and O atoms also presents interesting features. The various substitutions are able to yield ferromagnetic structures with semiconducting (AlO), metallic (N-Pt), or half-metallic (Al-Pt) ground states. These properties can lead to possible applications in spintronics and nanoelectronics. (C) 2015 Elsevier B.V. All rights reserved.