Recent progress of gene manipulation techniques enables us to insert foreign gene into human cells. This approach, so called gene therapy, is very attractive to treat molecular disease including congenital disorders or cancer. There have already been started 15 clinical protocols regarding gene therapy as well as gene-marking mainly in U.S.A., In this reviewing article, we introduce the public opinion about the gene therapy in Japan comparing with that in western countries. We then introduce the current clinical protocols about gene therapy and gene marking. We also discuss the future prospects of gene therapy. The progress in this field may cast a new light on the treatment of congenital disorders as well as cancers.