sensitive UPLC-MS/MS method was provided hereby to determine the concentration of salvianolic acid B in mice tissues after intravenous administration of salvianolic acid B injections, conventional liposomes and long-circulating liposomes. The UPLC was conducted by a C18 column with a gradient mobile phase consisting of acetonitrile and water containing 0.1% formic acid. The tandem mass spectrometry was operated in negative-electrospray ionization selected-reaction-monitoring mode, and the optimized characteristic precursor to product ion transition m/z 717.3 [right wards] 519.1 was selected. The biosamples were homogenized and treated with a protein precipitation, which led to an acceptable matrix effect and extraction recovery. The linear calibration curves were plotted in the given concentration ranges. The intra-day and inter-day precisions were less than 13.9% and the accuracies were in the range of 86.3-109.2%. The tissue distribution results determined by UPLC-MS/MS we developed showed that the conventional and long-circulating liposomes we made had succeeded in prolonging the retention time and increasing the level of salvianolic acid B in certain distribution tissues such as liver, kidney and brain