Cr-doped ZnO thin films have been prepared on silicon (100) substrates by a radio-frequency (RF) magnetron sputtering method. The crystallographic structures, optical, and magnetic properties of the thin films are investigated by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and physical properties measurement system (PPMS), respectively. The XPS results confirm that the chemical-bonding state of the doped Cr ions is +3. XRD analyses reveal that the Cr ions successfully replace Zn atoms and incorporate into the crystal-lattice positions of ZnO. Magnetic measurements reveal that all the samples have ferromagnetic features and saturation magnetization increases on increasing the dopant concentration. Room-temperature PL spectra show an ultraviolet (UV) emission at 380 nm and a green emission at 500 nm, whose intensity is greatly increased with increased Cr dopant. Moreover, the results of PL further testify that ferromagnetism (FM) is an intrinsic property of the Cr-doped ZnO films and FM can be described by bound magnetic polaron (BMP) models with respect to defect-bound carriers.