Al and X (Sn, Cu, In) co-doped ZnO nanocrystals were obtained by a sol-gel process. Structural, electrical and optical properties of the samples were investigated by means of X-ray diffraction, electrical resistivity measurements, and UV-VIS spectroscopy, respectively. Depending on co-dopant element, significant changes were observed in structural properties. A correlation was established in terms of tensile strain between microstructure, optical and electrical properties. By adding the co-dopant elements, tensile strain significantly became larger than that of undoped ZnO. Doping of ZnO with these co-dopants was found to degrade transmittance of the ZnO. The average transmittance which dramatically decreases with co-dopants was found to be correlated with calculated tensile strain. It was obtained to be nearly as 39 % for Al-Cu co-doped ZnO in visible range which was the lowest among others. Resistivity was observed to decrease upon the tensile strain, contrary to expectation. It reduced from 660 Omega cm of ZnO to 6.36 Omega cm with Al and In co-dopants.