Cesium ions doped yttrium aluminum garnet (Y2.96Al5O12∶0.04Ce3+) phosphors for white light emitting diodes (WLED) were successfully prepared by hydrothermal-thermolysis method. The phase composition, morphology, and photoluminescent properties of the prepared powders were investigated by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and photoluminescence spectroscopy. The results indicated that the successful preparation of the pure Y2.96Al5O12∶0.04Ce3+ powders are spherical particles and have good dispersibility. The phosphors were excited by the blue light with wavelength of 460 nm, and a broad peak at 550 nm was observed in the emission spectrum. Moreover, the emission peak intensity of the YAG∶Ce3+ powders prepared by hydrothermal-thermolysis method was higher than that of the samples prepared by traditional high temperature solid state method. Furthermore, the quantum efficiency of the white LED produced by the phosphors and blue chip was measured by the integrating sphere coupled fluorescence spectrometer, and the results indicated that the absolute quantum efficiency and external quantum efficiency of Y2.96Al5O12∶0.04Ce3+ phosphors prepared by hydrothermal-thermolysis method were 88.40% and 78.64%, respectively, with the color coordinates of (0.453 8, 0.531 8) and the color temperature of 358 4 K. The prepared Y2.96Al5O12∶0.04Ce3+ phosphors exhibited excellent stability and repeatability, and acted as excellent yellow phosphors for warm white LED.