The peels of Carya cathayensis Sarg. (PCCS) were treated under subcritical water conditions ($130^{circ}C$ to $280^{circ}C$ for 0 to 120 min). The extract from PCCS included reducing sugar, proteins, and compounds with radical scavenging activity. Addressing the reducing sugar that is a resource of bioethanol, we could maximize the reducing sugar under the subcritical water ($190^{circ}C$ for 60 min) and obtain 0.24 g/g-sample together with 9.7 units/mg-sample of radical scavenging activity. The obtained extract was estimated to correspond to 1 L of bioethanol/100 g-sample. It was therefore considered that the treatment by subcritical water could yield reducing sugar and natural compounds with radical scavenging activity.