CaSi2N2O2 codoped with Ce (fixed) and varying Tb concentrations were prepared by solid-state synthesis method. Crystalline phase was investigated by powder X-ray diffraction, the Tb, Ce-codoped CaSi2N2O2 phosphors have the monoclinic structure. Excitation spectra and emission spectra were investigated by spectrometer. The results indicated that there were two emission bands centered at 542 nm and 410 nm when excited by 360 nm, which were ascribed to the characteristic emissions of the Tb3+ and Ce3+. Monitored at 542 and 410 nm, respectively, the overlapped excitation spectra were obtained. Moreover, this excitation spectrum of Ce3+ overlapped perfectly with the excitation spectrum of Tb3+. As a result, the energy transfer from Ce3+ to Tb3+ was observed. The results of sample color coordinate analysis show that the Ca0.995-ySi2O2N2 0.005Ce3+, yTb3+ (y=0.06, 0.08, 0.10) is a single host phosphor with superior properties for white light emitting diodes.