Abstract: Bi (III) could catalyze the oxidation reaction between K₂S₂O₈ and methylene blue (MB), causing the dramatical quenching of the room temperature phosphorescence (RTP) signal of MB, and the ?IP of the system was linear to the content of Bi(III). Thus, solid substrate room temperature phosphorescence (SSRTP) for the determination of trace Bi (III) has been established. The linear range of this method was 0.040~1.0×10^–15 g/mL, the regression equation of working curve was ?I_P=2.336+27.26×10^–15C_Bi³⁺(g/mL)，n=6，correlation coefficient (r) was 0.9980，and detection limit (LD) was 1.9×10^–15 g/mL. This sensitive, simple and rapid method has been applied to determine trace Bi(III) in water samples with satisfactory results. The reaction mechanism was also discussed.