In order to investigate the inter-relation with the growth of the rice-toot and its mansaminase-activity, by measuring the growth of its root and transaminase-activity supplying this root with various nitrogen compounds(NO₃-N, NH₄-N and Amino acid.). The obtained results are summarized as follows; 1. Growth of rice-root supplied with NO₃-N is generally increased in length and weight, compared with that of the root fertilized by NH₄-N. 2. The above-mentioned root with NH₄-N is not only decreased in its weight and length but also is apt to inhibited in growth as the nitrogen concentration is increased, in compared with the root provided with NO₃-N. 3. The activity of G.O.T. and G.P.T. for the root fertilized by NH₄-N, the badly grown root is generally increased, while of the root supplied with NO₃-N is decreased. 4. The activity of G.O.T. and G.P.T. for the root provided with amino acid known as the considerable growth inhibiting compound is generally decreased, while that of the badly-grown root is increased. 5. The activity of G.O.T. and G.P.T. in the supermatant fraction of the rice-root is for the most part, high and low in the mitochondrial fract on.