Al doped ZnO(AZO) thin films were deposited at different substrate temperatures by a continuous composition spread(CCS) method. Various compositions of Al doped ZnO thin films deposited at substrate temperatures between 0 and $250^{circ}C$ were explored to find excellent electrical and optical properties. The AZO thin film deposited at $100^{circ}C$ had the lowest resistivity, $9{ imes}10^{-4}{Omega}$ cm and its average transmittance at the 400 to 700 nm wavelength region was 92 %. Optimized composition of the AZO thin film which had the lowest resistivity and high transmittance was 3.13 wt% Al doped ZnO.