Pulsed-laser deposition of undoped and Al-, Ga- and In-doped ZnO thin films is reported. The structure of the films remained unaffected by doping. The effect of doping on the optical and transport properties of the films was investigated. The band gaps, the optical constants, and the electron concentrations of the ZnO films are obtained from the ellipsometry and spectrophotometry data. Blue shift of the band gap due to doping is observed. The Burstein-Moss effect is remarked in the Ga- and In-doped ZnO films. The transport data show the increase of conductivity and mobility by doping with Al, Ga, or In. A number of deep levels with energies ranging from 0.75 to 1.14 eV are found in the ZnO films by photoconductivity measurement.