The γ-radiolysis of cellobiose (10 -2 M) in N 2 O saturated aqueous solution has been investigated and the G-values of the following 21 products containing six or less C-atoms have been measured (G-values in parentheses): glucose (2.1), gluconic acid (0.70), 4-ketoglucose (0.07), 5-keto-glucose (0.05), 4-deoxy-glucose (0.27), 5-deoxy-gluconic acid (0.18), 2-deoxy-gluconic acid (0.13), 3-deoxy-4-keto-glucose (0.23), 2-deoxy-5-keto-glucose (0.34), 4-deoxy-5-keto-glucose (0.14), 6-deoxy-5-keto-glucose (0.02), arabinose (0.07), ribose (0.015), 2-deoxy-ribose (0.17), 3-deoxy-pentulose (0.01), erythrose (0.015), threose (0.015), 2-deoxy-tetrose (0.01), butanone-(2)-diol(1.4) (0.01), dihydroxyacetone (0.01), carbon monoxide ( > 0.02). The formation of the major part (98%) of the measured products could be explained on the base of the following assumption: The first step of reaction sequence is abstraction of H atoms from C-Η bonds of the cellobiose by OH radicals. Radicals at C-1′, C-5′ and C-4 and their successors undergo in a second step four types of reactions: hydrolysis, rearrangement and H 2 O and CO elimination. In a third step the transformed radicals give rise to products by disproportionation reaction. Only two products out of 16 predicted under the above assumption are not observed. G-values for the attack at C-1′, C-5′ and C-4 are 1.4, 0.6 and 0.3 respectively.