Objective To investigate the change of the platelet parameter and to study the therapeutic effects of ulinastatin (UTI) on platelet parameter in patients with acute pancreatitis (AP). Methods The data of 80 patients with AP were analyzed retrospectively. All patients were divided into two groups: mild acute pancreatitis (MAP, n=43) and severe acute pancreatitis (SAP, n=37). Thirty people who took the medical examination and whose results were normal were included as control group. The autocytometer was used to test PLT, PCT, MPV and PDW in different periods of SAP. Results On admission, there were no significant differences of PLT, PCT between MAP group and control group (Pgt;0.05), but MPV and PDW in MAP group were higher than those of control group (plt;0.05). Compared with MAP group, PLT and PCT decreased markedly in SAP group (plt;0.01), while MPV and PDW significantly increased (plt;0.05). After 1-week treatment of UTI, PLT and PCT in MAP group didn’t change dramatically, while MPV and PDW decreased significantly (plt;0.05). While in SAP group, PLT and PCT increased significantly (plt;0.05, plt;0.01), and MPV and PDW decreased significantly (plt;0.01, plt;0.05). Compared with conventional treatment， PLT and PCT in MAP group increased significantly in UTI treatment group （plt;0.05）, but there was no statistical difference in terms of MPV and PDW （Pgt;0.05）. However, SAP group showed significant increase of PLT and PCT （plt;0.01， plt;0.05） and decrease of MPV and PDW in UTI treatment group compared with patients treated by conventional methods （plt;0.01）. Conclusion The platelet parameter changes in patients with acute pancreatitis, and the changes of SAP patients are more mark than those of MAP patients. UTI can significantly increase PLT and PCT, and significantly decrease the activity of the platelet. Therefore, UTI may take a role in the treatment and prevention for SAP.