To establish a rapid quantification method for heparinase Ⅰ dtring its production in recombinant Escherichia coli, a translational fusion vector was constructed by fusing the N terminus of heparinase Ⅰ to the C terminus of a green fluorescent protein mutant (GFPmut1). As a result, not only was the functional recombinant expression of heparinase Ⅰ in E. coli accomplished, but also a linear correlation was obtained between the GFP fluorescence intensity and heparinase Ⅰ activity, allowing enzyme activity to be quantified rapidly during the fermentation.