Objective To investigate the efficiency of intraclot microbubbles (MB) combined with urokinase (UK) mediated ultrasound (US) thrombolysis.Metho ds Fifty clots prepared by bovine whole blood were equally divided into 5 groups and were treated in a circulation system with collateral circulation tube.The clots were treated by US,MB and UK in group 1,by US and MBingroup 2,by US and UK in group 3 and by UK in group 4.The group5 was the control group without any treatment.The thrombolysis rate of each group was measured and compared.Residual clots were histologically observed with hematoxylin-eosin staining and immunofluorescence.Results The thrombolysis rate of group 1 ([73.64±14.16]％) was significantly higher than group 2 ([47.97± 11.66]％),group 3 ([57.33±8.65]％),group 4 ([50.85±9.63]％),and group 5 ([29.76±18.06] ％,all P＜0.05).Histological examination of the clots in group 1 showed multiple thrombolysis foci with clots collapse,and the degradation of fibrin network was further confirmed by immunofluorescence.Conclusion The intraclot MB mediated US thrombolysis combined with UK can enhance the rate of thrombolysis in vitro experiment.