OBJECTIVE： To establish a method for the content determination of main ingredient in naproxen solid lipid nanoparticles. METHODS： Microemulsion method was used to prepare naproxen solid lipid nanoparticles， and HPLC was used for the content determination. The column was Elite C18 with mobile phase A of methanol and B of 0.01mol/L KH2PO4 buffer solution （adjust pH to 3.0 by phosphoric acid）（gradient elution） at a flow rate of 1.0 ml/min， detection wavelength was 240 nm， column temperature was 25 ℃，and injection volume was 20 μl. RESULTS：The linear range of naproxen was 0.2-180.0 μg/ml（r＝0.999 7）； RSDs of precision， stability and reproducibility were lower than 1.00％； recovery was 99.73％-100.29％（RSD＝0.20％，n＝9）. CONCLUSIONS： The method is simple， accurate， and can exclude the accessories’ interference in naproxen solid lipid nanoparticles， which is suitable for the content determination of main ingredient.