Abstract: Based on the on-line reduction of molybdenum(Ⅵ) to molybdenum(Ⅲ) at the potential of -0.60 V(vs.Ag/AgCl), and the chemiluminescence (CL) reaction of luminol with molybdenum(Ⅲ) in alkaline condition, a method of flow injection-electrochemiluminescence for the determination of trace amount of molybdenum in coal ash was proposed. Linear relationship between values of increase in CL intensity and mass concentration of molybdenum(Ⅵ) was obtained in the range of 5.0×10-7-5.0×10-4g·L-1, with detection limit (3s/k) of 5×10-8g·L-1. Values of RSD (n=11) obtained for molybdenum(Ⅵ) at a concentration of 1.0×10-6g·L-1 was 2.6%. The proposed method was applied to the determination of molybdenum in coal ash, giving results in consistency with those obtained by the GB standard method.