To allow the ZnO nanorod arrays in new thin film solar cells to capture photons and to collect carriers effectively, a method to improve the conductivity of the ZnO nanorods and to control their optical properties was researched. Al-doped ZnO nanorod arrays were prepared by electrodeposition in aqueous solutions with Zn(NO3)2, NH4NO3 and Al(NO3)3. The experimental results indicate that the properties of ZnO nanorods such as the diameter, density and distance could be adjusted by controlling the NH4NO3 concentration in the electrolyte. The use of NH4NO3 in the solution leads to an increase of the Al/Zn weight ratio in the ZnO nanorods. By controlling the NH4NO3 concentration in the solution, the optical band gap of ZnO nanorod can be adjusted between 3.72—3.76 eV, and the optical properties of the nanorod such as the transmission, reflection and absorption can be controlled. The Stokes shift of the Al-doped ZnO nanorods was in the range of 377—449 meV, indicating the nonradiative recombination in the nanorods. Therefore the use of NH4NO3 in the electrolytes has successed in enhancing the Al doping in the ZnO nanorods and controlling their optical properties.