The present work concentrates on the synthesis of cubic ZnS and hexagonal ZnO semiconducting nanoparticle from same precursor via co-precipitation method. The phase conversion of ZnS to highly crystalline hexagonal ZnO was done by heat treatment. From the analysis of influence of calcination temperature on the structural, optical and vibrational properties of the samples, an optimum temperature was found for the total conversion of ZnS nanoparticles to ZnO. Role of quantum confinement due to finite size is evident from the blue shift of the fundamental absorption in UV-vis spectra only in the ZnS nanoparticles. The semiconducting nature of the prepared samples is confirmed from the UV-vis, PL study and transport study. From the magnetic and transport studies, pure ZnO phase was found to be more prone to magnetic field. (C) 2016 Elsevier Ltd. All rights reserved.