ObjectiveTo review the current status and advances of in vivo nucleic acid del ivery mediated by poly(ethylenimine) (PEI). MethodsThe related home and abroad literature about nucleic acid del ivery with applications in cancer treatments and tissue engineering was extensively reviewed and analyzed. ResultsA variety of in vivo study on the potential of PEI-mediated nucleic acid del ivery has been carried out and made certain effects in the animal model, ranging from cancer treatments to rectification of physiological defects (eg. cranial defect and corneal epithelium defect). Tail vein injection is the most commonly adopted route of administration in vivo, followed by pulmonary administration and intralesional injection. However, transfection and expression in vivo have some shortcomings, such as low transfection efficiency and short expression time, so there are some limitation in the cl inical application. ConclusionPEI mediated nucleic acid del ivery provides a good method for cancer treatments and rectification of physiological defects. For future research, not only should more in vivo animal testing be done, but the procedures of experimentation also need to be standardized.