Large part of urban area of around Kobe city were damaged by the 1995 Hyogoken-nanbu earthquake. For detecting the damaged area, the authors computed correlation coefficients from single-look complex ERS-1/SAR data. Two types of correlations, intensity correlation and coherence were computed. Decorrelation was found in the damaged urban built-up area in the data pair of which interval included the earthquake occurrence. The similarity of the decorrelation between the intensity correlation and the coherence indicated that major factor of the decorrelation is closely related to interferometric processes, which results in the change of speckle patterns in the single-look intensity images. A normalized difference was calculated from the correlation coefficients between the data pair including the earthquake occurrence and the pair before the earthquake. The distribution patterns of the pixels for which normalized difference was higher than a threshold showed good correspondence with the result of the ground survey. The result of this study indicates the possibility of detecting urban disasters using the decorrelation of SAR data.