We examined the reliability of prompt gamma-ray intensities by measuring ratios of thermal neutron capture cross sections on Na-23, Al-27, V-51, Mn-55, Ni-64, Cu-65, Pr-141, W-186, and Au-197 at the Kyoto University Research Reactor Institute. The cross sections were obtained by two methods: the first is detecting prompt gamma-rays (which we call the prompt-gamma method), and the other is detecting gamma-rays following P-decay (the activation method). Intensities of prompt gamma-rays and decay gamma-rays have been reported to have an uncertainty of about 5% and 1%, respectively. It is found that values of Cu-65 and (186) W have large discrepancies in the results of the two methods, by about 30%. The disagreement would be caused by inaccuracy of the absolute intensities of prompt gamma-rays. The inaccuracy is estimated to be due to the incompleteness of level schemes and the detector efficiency of prompt gamma-rays. We need to examine absolute intensities of prompt gamma-rays when we use the prompt-gamma method.