Abstract: Based on the sensitization effect of thiourea on the CL-reaction system of luminol-H2O2-silver nanoparticles in NaOH medium, a method for the determination of thiourea by FI-chemiluminescence (CL) was proposed. Under the optimum conditions, linear relationship between values of CL intensity and concentration of thiourea was obtained in the range of 4.0×10-8-4.0×10-6mol·L-1 with detection limit (3σ) of 3.0×10-9mol·L-1. The proposed method was applied to the analysis of sample of orange juice, giving values of recovery by standard addition method in the range of 95.7%-105.3% and values of RSD (n=6) in the range of 1.8%-3.2%.