ZnO nanostructures are wide band gap semiconductors well established especially for optoelectronic applications. The addition of transition metals to the ZnO crystal lattice is known to create new energy levels below the conduction band, which changes the electronic structure of ZnO. The band gap tuning of ZnO can be achieved through dopant concentration variation. Apart from the notable changes in optical properties, the amount of dopant is found to affect the structural, and photocatalytic properties of the doped oxide. Doping ZnO with transition metals can also improve its photocatalytic activity. Some transition metals that can be used to dope ZnO include Mn, Fe, Co, Ni, and Cu. The present study shows the synthesis of nanostructured ZnO doped with transition metals such as Mn, Co and Cu. The structural, morphological and optical studies are discussed. The transition metal doping was found to tune the bandgap of ZnO towards a red shift. The band gap narrowing and observed red shift is due to the exchange interactions, confirming the substitution of dopants into the ZnO lattice.