In this paper, we report modifications of structural and optical, electrical properties that occur in tin sulphide (SnS) treated in O-2 plasma. The SnS thin films were deposited by chemical bath deposition technique. The samples were treated in an O-2 plasma discharge at 3 Torr of pressure discharge, a discharge voltage of 2.5 kV and 20 mA of discharge current. The prepared and treated thin films were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis. The photo-conductivity and electrical effects of SnS have been studied. The SnS thin films had an orthorhombic crystalline structure. With the plasma treatment the optical gap and electrical properties of the SnS films changed from 1.61 to 1.84 eV, for 3.9 x 10(5) to 10.42 Omega cm, respectively. These changes can be attributed to an increase in electron density, percolation effects due to porosity, surface degradation/etching that is an increase in surface roughness, where some structural changes related to crystallinity occurs like a high grain size as revealed by SEM images. (C) 2012 Elsevier B.V. All rights reserved.