Using a low frequency ultrasonic flow detector and an X-ray-computed tomograph, we determined whether it would be possible to carry out non-destructive measurement of a watercore in the Japanese pear ‘Hosui′. The traveling speed of the longitudinal ultrasound waves of the low frequency ultrasonic flow detector was found to be higher with increased development of the watercore in fruits with ground color values of the calyx end below 3.5, based on a color chart for Japanese pear ground color^{6, 12)}, but not in fruits with a ground color value above 3.5. On the other hand, using an industrial X-ray-computed tomograph, the photographs of the fruits with watercore represented by white points that were obtained by selecting CT-values from +0020 to +0050, nearly corresponded to the extent of the development of the watercore. The results obtained indicate that X-ray-computed tomography could be used for non-destructive measurement of the occurrence of a watercore in the Japanese pear Hosui.