Since the viral vector for gene therapy has serious problems, including oncogenesity and other adverse effects, non-viral carriers have attracted a great deal of attention. However, the most critical issue of gene delivery by non-viral carriers is the low-expression efficiencies of the desired gene. In order to apply non-viral carriers for gene therapy in practical clinical usage, the improvement of transfection efficiency is a prerequisite. We will summarize the current progress of non-viral delivery systems for gene therapy. Especially, we will address the applications of cationic lipids (lipoplex) and cationic polymers (polyplex) in vivo. Furthermore, there have been reported a disease-site-specific delivery system which responds to highly activated cellular signals, which is called a drug delivery system based on responses cellular signal (D-RECS). We will also introduce the current progress of D-RECS gene delivery which is activated by HIV protease in only HIV-infected cells.