A synthetic nucleic acids fragment encoding the GPRP peptides was linked with the scu-PA (144-411) cDNA at its 5' end, and was subsequently inserted into the expression vector pKK233-2 and expressed in E. coli with a level of 5% of the total bacterial proteins. The expressed product of GPRP-scu-PA (144-411) cDNA was purified by affinity chromatography. Its < italic>K(m) was 40 &mgr;M, with the clotlysis rate 2-3 times of that of LUK, and the fibrin affinity 6 times higher than that of LUK. At the same time it had a low affinity for fibrinogen. These results showed that the GPRP peptide fragment was able to improve the fibrin-specific affinity of urokinase.