Hydrocortisone (HC)-loaded rosin nanoparticles were prepared by a dispersion and dialysis method without addition of surfactant. They were spherical: 167-332 nm diam. The drug was loaded approximately 50% of initial feeding amount in all formulation. Release of hydrocortisone from the nanoparticles in vitro gradually decreased with increasing initial rosin content at pH 7.4. HC was also released very slowly at pH 1.2. Nanoparticles based on rosin thus are potentially useful as a drug delivery system.