Ternary polycrystalline Cd-doped ZnO semiconductor thin films with cad mium content (x) ranging from 0to 0.23were obtained on quartz substrate by pulse laser deposite d (PLD) technique. X-ray diffraction (XRD) measurement reveals that all the films are single pha se of wurtzite structure grown on c-axis orientation with its c-axis lattice constant increasing as the Cd content x increasing.The increase of lattice constant is due to the fact that the covalen t radius of Cd²⁺ is larger than that of Zn²⁺,and therefore the substitution of Zn²⁺ ions by Cd²⁺ ions induces a lattice volume expansion.Atomic force microscopy (AFM) observatio n reveals that the grain size of Zn1－xCdxO films decreases continuously as the Cd content x increases.Bo th photoluminescence(PL) and optical measurements show that the band gap de creases from 3.27eV to 2.78eV with increasing the Cd content x,which can be interpreted in terms of band gap modul ation due to Cd doping.Increasing the Cd content x also leads to the bro adening of the emission peak.The broadening and other small peaks result from various crystalline defects.The shift o f PL emission to visible light range makes the Zn1－xCdxO films to be potential candidate for optoelectronic devices.