Abstract: Sulfur quantum dot (S QDs) of about 4 nm with a strong fluorescence property were prepared by means of oxidizing sublimed sulfur for a long time with nitric acid. The electrochemiluminescence(ECL) response behavior of the S QDs mixed with Ru(bpy)₃²⁺ for sarcosine was investigated. It is found that the same concentration of sarcosine has the strongest signal sensitizing effect on S QDs/Ru(bpy)₃²⁺; system compared with that of Ru(bpy)₃²⁺ or S QDs alone as luminescent reagent. Based on this, a new method for determining sarcosine was constructed. In 0.1 mol/L PBS (pH=8.0), the difference value of ECL increased linearly with the increase of concentration of sarcosine in the range of 1.0×10^-7 -8.0×10^-5 mol/L, the detection limit is 5.0×10^-8 mol/L. The relative standard deviation for 10 times determination of 8.0×10^-5 mol/L sarcosine was 3.04%, which shows this method has a good reproducibility and stability. Additionally, this method was applied to the determination of sarcosine concentration in dilute urine with a satisfactory reproducibility, which provides an evident of developing an detection method for sarcosine in samples.