AIM: To prepare the chitosan-pmEpo nanoparticles and to study their ability for transcellular and paracellular transport across intestinal epithelia by oral administration.METHODS: ICR mice were fed with recombinant plasmid AAV-tetO-CMV-mEpo (containing mEpo gene) or pCMVβ (containing LacZ gene), whether it was wrapped by chitosan or no. Its size and shape were observed by transmission electron microscopy. Agarose gel electrophoresis was used to assess the efficiency of encapsulation and stability against nuclease digestion. Before and after oral treatmant, blood samples were collected by retro-orbital puncture, and hematocrits were used to show the physiological effect of mEpo.RESULTS: Chitosan was able to successfully wrap the plasmid and to protect it from DNase degradation. Transmission electron microscopy showed that freshly prepared particles were approximately 70-150 nm in size and fairly spherical.Three days after fed the chitosan-pCrvlVβ complex was fed,the mice were killed and most of the stomach and 30% of the small intestine were stained. Hematocrit was not modified in naive and ′naked′mEpo-fed mice, a rapid increase of hematocrit was observed during the first 4 days of treatment in chitosan-mEpo-fed animals, reaching 60.9±1.2% (P＜0.01),and sustained for a week. The second feed (6 days after the first feed) was still able to promote a second hematocrit increase in chitosan-mEpo-fed animals, reaching 65.9±1.4%(P＜0.01), while the second hematocrit increase did not appear in the ′naked′ mEpo-second-fed mice.CONCLUSION: Oral chitosan-DNA nanoparticles can efficiently deliver genes to enterocytes, and may be used as a useful tool for gene transfer.