The chemical composition of amino acids in the rind and fresh of Citrus Junos Sieb was studied and compared with that of Citrus natsudaidai Hayate. The results were summarized as follows. 1. Beth of them contained twenty kinds of amino acids, including three kinds of unknown amino acids. 2. Proline in the rind of Citrus Junos and aspartic acid in the rind of Citrus natsudaidai were the richest of all amino acids but on the contrary. Histidine was the poorest of all amino acids in the rind of them. The content of proline amounted to 16.48 mg/100mg in the rind of Citrus Junos and the content of aspartic acid amounted to 32.18 mg/100mg in the rind of Citrus natsudaidai. 3. Aspartic acid was the richest of all amino acids in the flesh of Citrus Junos and the content of it amounted to 32.68mg/100mg. On the other hand, Proline was the richest of all amino acids in the flesh of Citrus natsudaidai and the content of it amounted to 20.93mg/100mg. But the content of histidine as 1.32 mg/100 mg in the flesh of former and tyrosine as 1.18 mg/100 mg in the flesh of latter were relatively small. 4. In the fruits of Citrus Junos and Citrus natsudaidai, aspartic acid and Proline were rich and histidine was poor in quantity. Generally, Flesh contained more amounts of all kinds of amino acids than those rind and especially glutamic acid was richer, compared with other amino acids in flesh.