Abstract--Rice is the staple food for most Indonesian people and the rate of rice consumption is increasing every year, eventhough government should go import. The source of carbohydrates not only from rice, but there are many other materials such as cereals, tubers that have not been threated optimally. Similarly, the occurrence of a shortage of protein in some communities in Indonesia are still being found. Therefore, the strategy of this problem is with food diversification to substitute or replace the rice needs by using rice analog from Nagara beans (Vigna unguiculata ssp Cylindrica). Nagara beans have high carbohydrate content about 50-60% and 20-25% protein. This research was aimed to modify Nagara bean flour through spontaneous fermentation with variation of bean size and periods of fermentation. Fermented Nagara bean flour were tested several parameters which include yield, moisture content, bulk density, protein content, water absorption capacity, swelling volume, and solubility. Nagara beans contain amino acid dominant aspartic acid 0.913%, glutamic acid 2.182% and histidine 0.826%. Grits size produce flour yield, protein content, water absorption capacity, and the swelling volume greater than others. Fermentation time up to 120 hours tend to lower flour yield and protein content, while the water absorption capacity tend to increase up to 96 hours fermentation and swelling volumer tends to be stable up to 96 hours fermentation periods. Keywords : nagara bean flour, spontaneous fermentation, protein, water absorption capacity