UV filters are traditionally classified as chemical absorbers and physical blockers depending on their mechanism of action. In this study, one of the most important chemical UVB absorber, octocrylene, was incorporated into Solid Lipid Nanoparticle (SLN) systems which themselves have UV blocking potential similar to physical blockers. Determination of octocrylene in the formulations was performed by HPLC (High Performance Liquid Chromatography) using a new validated method based on ICH harmonised tripartite guideline validation of analytical procedures Q2(R1). Determination and validation studies were carried out on a 4.6 x 250 mm, 5 microm C18 ACE column using an optimized mobile phase of acetonitrile:water (75:25, v/v) at a flow rate of 1.5 mL x min(-1). UV detection was performed at 210 nm and the column temperature was adjusted to 50 degrees C. Cyclosporine A was used as an internal standard (IS). The specified working range was derived from linearity studies and kept in the concentration range of 2.5 x -5.5 x 10(-5) M. Good correlation and accuracy were obtained. Limit of detection (LOD) and limit of quantitation (LOQ) values were determined to be 1.64 x 10(-6) M and 4.97 x 10-6 M, respectively. Octocrylene recovery % results of the SLN formulations stored at 25 degrees C, 4 degrees C and 40 degrees C for 360 days were investigated and compared to the freshly prepared samples.