Objective: To evaluate the application of micro-flow imaging(MFI) in the detection of particulate matters in biochemical protein drugs(urokinase for injection), and to investigate the status of particulate matters in urokinase samples for injection from various manufactures, and the differences of particulate matters after resolution with two different solvents, and find out the main origin of particulate matters. Methods: The urokinase for injection was re-dissolved in either sterilized water for injection or sterilized normal saline for injection respectively, and the particulate matters were analyzed by MFI. The MFI methodology was validated, comparing with light obscuration method. Results: For 5 μm and 15 μm particulate standard detected by MFI, the counting accuracy(deviations) of particle count were 11.6% and 8.5%, precision(RSDs) were 1.6% and 3.8%, the accuracy (deviations) were 2.5% and 0.8%, precision(RSDs) were 0.6% and 0.1%. In the results of determination of particulate matters detected by MFI with the particle size of 2-10 μm were mainly proteinaceous, and the partide size of more than 10 μm were mainly non-proteinaceous. The result of non-proteinaceous particulate matters detected by MFI was similar to light obscuration method. The particulate matters in urokinase for injection produced by different manufactures were quite different, and the particulate matters for manufacturer A was more. There was no significant difference in the results of particulate matters after dissolved with two different solvents for samples from manufacturer A and C, and significant difference for samples from manufacture B and D. Particulate matters were less for samples re-dissolved with sterilized normal saline. Conclusion: MFI was first applied to detect particulate matters in biochemical protein drugs (urokinase for injection). It provides new ideas for exploring the source of particulate matters in biochemical protein drugs. The results of particulate matters in individual manufactures were close to the limit, suggesting that the manufactures need to strengthen research and development to improve product quality control. And manufactures can analyze the main sources of particulate matters from endogenous and exogenous cause according to the result of 2-10 μm range and particle size more than 10 μm.Reconstitution with different two solvents affected the results of particulate matters for some samples, and particulate matters are less for samples dissolved with sterilized normal saline. But the cause of the above results need further study.