Using the solid-state reaction method, Ce3+,Tb3+-coactivated Si5AlON7 (Si6−zAlzOzN8−z, z = 1) phosphors were successfully synthesized. The obtained phosphors exhibit high absorption and strong excitation bands in the wavelength range of 240–440 nm, matching well with the light emitting-diode (LED) chip. The ET from Ce3+ to Tb3+ ions in Si5AlON7:Ce3+,Tb3+ has been studied and demonstrated by the luminescence spectra and decay curves. Moreover, the phosphors show tunable emissions from blue to green by tuning the relative ratio of the Ce3+ to Tb3+ ions. Thermal quenching properties of Si5AlON7:Ce3+,Tb3+ had also been investigated and the quenching temperature is ~190°C. These results show that Si5AlON7:Ce3+,Tb3+ could be a promising candidate for a single-phased color-tunable phosphor applied in UV-chip pumped LEDs.