Abstract: In this paper, the moisture sorption isotherms of bamboo power, bamboo blocks, chemically macerated bamboo fibers and parenchymal cells were respectively established by measuring their corresponding adsorption equilibrium moisture content(EMC)at different relative humidity(RH)levels. The results indicate that all the established moisture sorption isotherms of bamboo are characterized with anti-S shaped curves, which is normally found in wood and wood composites. The moisture sorption isotherm of bamboo powder is as a whole located above that of bamboo blocks with a maxim value of 1.5% at 46% RH, however the difference at fiber saturation point(FSP)is only about 0.37%. The moisture content at FSP of bamboo fibers and parenchyma cells is 34.07% and 44.24% respectively, significantly higher than that of bamboo blocks and bamboo powders. It was explained that the chemical maceration facilitated the formation of multi-layer water adsorption and condensed water in the bamboo cell wall.