This investigation was carried out to justify the assignment of mungbean plant from the genus Phaseolus to the genus Vigna. Electrophoretic studies on seed storage proteins (albumin, globulin and total soluble proteins) using SDS-PAGE proved that mungbean plant is more related to cowpea plant with similarity of 21% compared with 9% between plants of mungbean and kidney bean, suggesting the assignment of mungbean plant to the genus Vigna. Further phytochemical studies were carried out to compare between plants of mungbean and cowpea. Percentages of the main chemical components in seeds were as follows: Total carbohydrates 67.93, 65.65; crude protein 23.90, 24.62; lipids 1.20, 1.30; fibres 4.07, 5.07; ash 2.90, 3.36 and moisture 6.06, 6.16% for mungbean and cowpea, respectively. Moreover, seeds of mungbean and cowpea positively shared the presence of 16 amino acids. These results strengthen the assignment of mungbean plant to the genus Vigna. Electrophoretic analysis of seed storage proteins, and main chemical components of seeds suggest that mungbean plant is more closely related to the genus Vigna. Hence the name Vigna radiata (L.) Wilczek might be accepted as the name of choice for mungbean plant. Morphological and anatomical features through the consecutive ages of 2 growing seasons of mungbean and cowpea plants are considered in the following two parts of this study as extra evidences in this concern.