Core/shell nanoparticles with lipid core were prepared and characterized as pH-sensitive delivery system of anticancer drug. The lipid core is composed of drug-loaded lecithin and the polymeric shell is composed of Pluronics (poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) tri-block copolymer, F-127). Based on the preparation method in the previous report by us, the freeze-drying of drug-loaded lecithin was performed in the F-127 aqueous solution containing trehalose used as a cryoprotectant to form stabilized core/shell nanoparticles. For the application of core/shell nanoparticles as a pH-sensitive drug delivery system for anticancer drug, doxorubicin was loaded into the core/shell nanoparticles and the drug loading amount and drug release behavior in response to pH change were observed.