The purified ${eta}-mannanase$ hydrolyzed various gums to mannose, ${eta}-1,4-mannobiose$, $Gal^3Man_4$, and D.P 7 of galactosyl mannooligosaccharide, and isolated from the enzymatic hydrolysate for 24 hrs reaction by activated carbon column chromatography and Sephadex G-25 column chromatography. For the elucidate of antioxidant action of ${eta}-1,4-mannobiose$, $Gal^3Man_4$ and DP 7 of galactosyl mannooligosaccharide and urea derivatives, coloration, reducing power, antioxidant activity and DPPH test were accomplished. The coloration was high at reaction mixture of ${eta}-1,4-mannobiose$, $Gal^3Man_4$ D.P 7 and urea. TLC of reaction mixture of ${eta}-1,4-mannobiose$, $Gal^3Man_4$ D.P 7 and ureas showed new reaction products, respectively. but except reaction mixture of ${eta}-1,4-mannobiose$ and urea. The reducing power was high at reaction mixture of ${eta}-1,4-mannobiose$, $Gal^3Man_4$ D.P 7 and phenylthiourea. The reaction mixture of ${eta}-1,4-mannobiose$, $Gal^3Man_4$ D.P 7 and thiourea showed similar radical scavenging activities on DPPH to activity of AsA. The reaction mixture of ${eta}-1,4-mannobiose$, $Gal^3Man_4$ D.P 7 and thiourea, phenythiolurea shown strong antioxidative activites on the oxidation of linoneic acid.