Abstract: The glycosylation heterogeneity of recombinant human pro-urokinase (pro-UK) was assessed using ultra-performance liquid chromatography-mass spectrometry (UPLC-MS). Firstly, the source of heterogeneity was determined by measuring the M_r of intact protein before and after N-deglycosylation. Glycosylation sites and the proportion of O-glycopeptides then were determined at the peptide level. Finally, the N-glycans were confirmed and quantified using the N-glycan profile. Results show that the structural heterogeneity of pro-UK is mainly caused by glycosylation. All T₁₈ were fucosylated, and 6.4% of S_138/139 was O-glycosylated with two kinds of oligosaccharides with a ratio of 6.0% and 0.4% respectively. All N₃₀₂ positions were N-glycosylated by more than ten types of glycans, among which A2F and A3F accounted for 80% of the total. The assessment of glycosylation heterogeneity of pro-UK will provide a reference for quality standardization.