Proximate compositions, quality and physicochemical characteristics of small black soybean cultivar, cultivated in the north-central region of South Korea with different seeding periods, were evaluated. Proximate compositions, chromaticity, water binding capacity, water solubility index, swelling power, and antioxidant properties were significantly different among cultivars and different seeding periods. Moisture, crude ash, fat, protein, and carbohydrate contents of small black soybean cultivar were 5.53~6.69, 5.47~6.54, 15.38~19.14, 34.17~40.26, and 32.04~36.85 g/100 g, respectively. Lightness, redness and yellowness were 35.60~38.61, -0.02~0.07 and -0.56~-0.13, and water binding capacity, water solubility index and swelling power were 84.48~148.31, 46.65~54.89 and 29.87~35.12%, respectively. Total polyphenol contents of first, second, and third seedings on small black soybean cultivar were 10.40~15.48, 9.86~14.85 and 8.61~15.39 mg GAE/g; total flavonoid contents were 5.81~7.25, 5.81~7.34 and 5.52~7.64 mg CE/g, respectively. DPPH radical scavenging activity was 4.55~7.86, 3.99~8.79, and 3.74~9.43 mg TE/g, and ABTS radical scavenging activity was 9.32~12.90, 8.64~13.39, and 8.51~14.35 mg TE/g, respectively. Phenol compound of Tawonkong and Socheong cultivars decreased with delay of seeding periods. Radical scavenging activity of Socheong and Jununi cultivars decreased with delay of seeding periods, but Socheong 2 and Socheongja cultivars increased. In the study, phenol compound and radical scavenging activity of small black soybean cultivar were different, depending on cultivars and seeding periods.