Nitrogen is a vital element for plant growth and development. The study on mechanism of nitrogen absorption by plants can help optimize nitrogen fertilization and may also serve as a theoretic foundation for breeding new cultivars with higher nitrogen use efficiency. Nowadays, with the recent development of interdisciplines scientists have begun to study mechanism of N assimilation using the technology of molecular biology. NH₄⁺ and NO₃^- are two major N sources for plants. In this article, researches on identification, cloning and expression patterns of AMT and NRT genes responsible for NH₄⁺ and NO₃^- assimilation, respectively, are briefly reviewed.