An amphiphilic core/shell-type polymer-based drug carrier system (HPAE-PCLb-MPEG), composed of hyperbranched poly(aminoester)-based polymer (HPAE) as the core building block and poly(ethylene glycol)bpoly(ε-caprolactone) diblock polymers (MPEGb-PCL) as the shell building block, was designed. The synthesized polymers were characterized with FTIR, 1 H NMR, 13 C NMR, and GPC analysis. Monodisperse HPAE-PCLb-MPEG nanoparticles with dimensions of <200 nm and polydispersity index of <0.5 were prepared by nanoprecipitation method and characterized with SEM, particle size, and zeta potential analysis. 5-Fluorouracil was encapsulated within HPAE-PCLb-MPEG nanoparticles. In vitro drug release profiles and cytotoxicity of blank and 5-fluorouracil-loaded nanoparticles were examined against the human colon cancer HCT116 cell line. All results suggest that HPAE-PCLb-MPEG nanoparticles offer an alternative and effective drug nanocarrier system for drug delivery applications.