Transgene, a concept becoming more and more widely used in modern molecular biology research, has been used to refer to all the foreign genes which were reconstructed and transfered by genetic engineering strategies, and then stably integrated into the genomes of higher eukaryotic cells. The types of transgene structure, its genetic behavior in the recipient cells, the characteristics of transgene expression,the factors involved in the expression regulation and the biological effects of the transgenes are reviewed. The unknown problems in the transgenie research are illustrated. The necessity of doing the systematical research about the molecular biological characteristics of the transgenes is pointed out.