In this article, a kind of biodegradable poly(epsilon-caprolactone)-Poly(ethylene glycol)-poly(epsilon-caprolactone) (PCL-PEG-PCL, PCEC) copolymer was synthesized by ring-opening polymerization method. The PCEC nanoparticles were prepared at one-step by modified emulsion solvent evaporation method using CTAB as stabilizer. With increase in PCEC concentration, the particle size increased obviously, but zeta potential only increased slightly. The obtained cationic PCEC nanoparticle was employed to condense and adsorb DNA onto its surface. Plasmid GFP (pGFP) was used as model plasmid to evaluate the loading capacity of cationic PCEC nanoparticles in this work. The DNA/nanoparticles weight ratio at 1:16 induced almost neutral zeta potential of DNA-nanoparticles complex. At this time, the size of complex became abnormally large which implied aggregates formed. So DNA-nanoparticles weight ratio should be chosen carefully. The cationic PCEC nanoparticles had the capacity of condensing plasmid DNA into complex when the DNA/nanoparticles weight ratio was lower than 1:8, which was evidenced by gel retardation assay. In vitro release behavior of DNA/nanoparticle complexes was also studied here. The obtained cationic PCEC nanoparticles might have great potential application in DNA delivery.