The 3-deoxy-n-pentosone (I) was isolated from the browning degradation mixture of N-n-xy1osy1-n-butylamine by the action of acetic acid at 55°C. The 3-deoxy-d-erythrohexosone (IIa) and the 3-deoxy-n-threohexosone (IIb) were also prepared by degradation of the corresponding N-glycosyl-n-butylamine. The 3-deoxy-d-pentosone was characterized as the 2,4-dinitrophenylosazone and its diacetate, and the p-nitrophenylosazone. The two 3-deoxy-d-hexosones were also characterized as the analogous derivatives. The three 3-deoxyosones gave positive color reactions with 2-thiobarbituric acid. As one of the intermediates in 3-deoxyosone formation from N-glycoside, 1,2-eno1 form of 1-deoxy-1-n-butylamino-2-ketose (IV) was proposed.