Abstract: AIMTo prepare long-circulating solid lipid nanoparticles containing paclitaxel with stearic acid, and investigate the in vitro and in vivo characterization of nanoparticles. METHODSThe method of “emulsion evaporation-solidification at low temperature” was used to prepare the stearic acid solid lipid nanoparticles containing paclitaxel. Its morphology was examined by transmission electron microscope. The HPLC method for determination of paclitaxel in nanoparticles or serum samples was established. The release of paclitaxel in vitro and the pharmacokinetics after iv bolus injection to mice were studied. RESULTSThe mean diameter of Brij78-SLN and F₆₈-SLN is (103.5±29.2) nm and (220±98) nm, respectively. The nanoparticles release paclitaxel slowly and linearly, within 24 h, Brij78-SLN and F₆₈-SLN release 8% and 20% of total drug, respectively. Long-circulation nanoparticles was found to stay in the blood circulation, with t_1/2β 10.1 h of F₆₈-SLN, and t_1/2β 4.88 h of Brij78-SLN more than one commercialized paclitaxel injection, t_1/2β 1.3 h. CONCLUSIONStearic acid might be a new drug carrier material in the future.