Objective To establish a reverse phase high performance liquid chromatography (RP-' HPLC ) method and to determine the encapsulation efficiency of zanamivir-loaded solid lipid nanoparticles (SLNs). Methods RP-HPLC analysis was performed on an Inertsil ODS-3 Cl8(250 ×4.6 mm,5 μm) column with mobile phase of acetonitrile-water(10: 90). The flow rate was 0.6 ml/min. The wavelength of UV detector was set at 235 nm and the injection volume was 20 μl. Zanamivir-loaded SLNs was prepared by a double emulsion solvent evaporation method. Transmission electron microscropy (TEM) was conducted to investigate the morphology of SLNs. The mean diameter and zeta potential of SLNs were measured by photon correlation spectroscopy. The entrapment efficiency and drug loading amount of SLNs were detected by RP-HPLC. Results It had a good linear relation in the range of 0. 5 ~ 100.0 μg/ml (r = 0.999 9). The intra-day precision ( RSD) was 0. 59% ~ 2. 03% ( n = 3 ). The inter-day precision (RSD) was 1.06% -1.88% (n=3). The average recovery rate was 100. 11% (n = 3). The SLNs were sphere like with the average size of (183. 9 ±5. 7)nm and zeta potential of(-53.0±1.6) mV. The encapsulation efficiency and drug loading amount of SLNs were (36.1 ±2.8)% and (0.32 ± 0.03) % , respectively. Conclusion The developed RP-HPLC method is simple, accurate and reliable for determination of entrapment efficiency of zanamivir-loaded SLNs.