The X-ray computed tomographic (CT) scanner was used to monitor the internal quality changes in peaches during ripening. The physicochemical constituents were monitored and the X-ray absorption expressed in CT number was used as an index. Relationships between the CT number and the physicochemical contents were determined. Results showed that CT number, moisture content and titratable acidity decreased significantly with postharvest ripening time, while pH and soluble solids increased with postharvest ripening time. The X-ray CT number is directly related with density, moisture content and titratable acidity. The soluble solids and pH are inversely related with CT number. X-ray CT imaging can be used as an effective tool in the evaluation of peach internal quality.