Grey brick is a key material in Chinese traditional architecture. The isothermal sorption curve of grey bricks is one of the basic moisture characteristics for studying the heat transfer of brick building enclosure structures and is also a fundamental parameter of research into the degradation mechanisms of Chinese traditional architecture. In this study, we measure the isothermal sorption curves of Wujiang (Suzhou, China) bricks from the 1980s and the late Qing period, by applying constant relative humidity controlled by saturated salt-water solutions under isothermal conditions. We then present their fitting formulas for humidity bound ranges of 5_92%. The results indicate that samples of the same-area traditional Suzhou grey bricks from different time periods show relatively large differences in their isothermal sorption properties, with the isothermal sorption property values of the late Qing grey bricks about three times those of the 1980s grey bricks.