We report the synthesis of inter-twinned ZnO nanowires doped with Mg2+ by electrospinning polyvinyl alcohol along with metal oxide precursors followed by heat treatment 650 degrees C for 3 h in air. Mg doping influences the morphology of the nanofibers as well as the structure and optical properties of the heat treated samples. Up to 5 wt% Mg doping, single phase wurtzite structure of ZnO is retained. Optical bandgap energy of ZnO nanowires could be tuned over the range of 3.25-3.56 eV by increasing Mg doping up to 8 wt%. Interestingly, defects present in undoped ZnO decreased drastically upon doping with Mg.