Sialons are widely recognized for their rigid lattice structure, high visible light transmittance, and excellent thermal stability, making them suitable matrix materials for activators. In this paper, we successfully prepared β-sialon phosphors, β-Si6-zAlzOzN8-z:Eu2+ (β-SiAlON:Eu2+), using an organic precursor method at a low synthesis temperature for the first time. X-ray diffraction analysis and Rietveld refinement confirm the β-SiAlON:Eu2+ phosphor possesses a hexagonal structure with a P63 space group. Under 320 nm excitation, β-SiAlON:Eu2+ phosphor exhibits a blue emission band centered at 415 nm due to the 5d → 4 f electron transition of Eu2+, which differs significantly from other β-SiAlON:Eu2+ phosphors with green emission. It is interesting that excessive Eu2+ activators make β-SiAlON:Eu2+ phosphor possess a green emission band centered at 510 nm. Therefore, the light-emitting color of β-SiAlON:Eu2+ phosphor shifts from the blue to the green with the increase of Eu2+ concentration. Furthermore, the activation energy of β-SiAlON:0.02Eu2+ sample is calculated to be about 0.2527 eV, which confirms β-SiAlON:Eu2+ phosphor has good thermal stability. The article presents a low-temperature and cost-effective synthesis method for preparing sialons, as well as a novel blue β-SiAlON phosphor for solid-state lighting.