Objective To prepare a self-microemulsifying drug delivery system of lapatinib, and to evaluate its quality in vitro and pharmacokinetic properties in rats.Methods Detect the lapatinib solubility in different excipients, and select appropriate excipients to complete ternary phase diagram, and optimize the formulation by central composite design-response surface methodology, Detect the particle size, Zeta potential of the prepared lapatinib microemulsion, and observe its microscopic morphology by transmission electron microscope. Examine the effects of different media, dilution ratio and storage time on the particle size of lapatinib microemulsion. The in vitro release test and pharmacokinetics test of lapatinib microemulsion and lapatinib suspension in rats were also performed here.Results The optimized lapatinib microemulsion was composed of corn oil∶oleic acid∶RH40∶TP=20∶20∶48∶12. The mean particle size of lapatinib microemulsion was (35.88±0.61) nm, Zeta potential was (-2.81±0.25) mV. The particle size of lapatinib microemulsion was still stable when diluted at 1∶50, 1∶100, 1∶200 in pH 1.0, pH 4.5, pH 6.8 medium respectively and placed for 6 h. The total lapatinib release was found to be 70% at the end of 48 h in the in vitro drug release studies. Compared to the lapatinib suspension, the C_max and AUC of lapatinib in microemulsion was significantly improved as showed in pharmacokinetic experiments of rats.Conclusion The self-emulsifying drug delivery system of lapatinib was stable. It could improve the solubility of lapatinib and the bioavailability in rats, and could be contribute to the development of new forms of lapatinib.