Alkaline phosphatase(AP)-labelled streptavidin (SA) is the most important general reagent in enzyme-amplified time-resolved fluo-roimmunoassay. A two step method of AP-labelled SA using glutaraldehyde was described. Characteristics of the labelled product AP-SA were measured using the self prepared fluorescence developing solution and the substrate-5-fluorosalicyl phosphate. The labelled recovery of AP is 38.7%.The relationship between diluting times of the AP-SA and signal/noise ratio of Tb³⁺ is linear when diluting the AP-SA 200～12 800-fold. Enzyme activity of the AP-SA is stable during two months at least.