Polymeric composites consisting of cellulose and poly(acrylic acid) (PAA) are prepared by coagulation/bulk polymerization method. Scanning electron microscopy and thermal gravimetric analysis are used to investigate the homogeneity and the heat-induced water loss of the composites, respectively. The water absorbed in the composites has strong hydrogen bonding with the polymer chains, as determined by differential scanning calorimetry. The mechanical and structural properties of the composites vary reversibly when the composites are applied into specifically explored wetdry cycles, which are comprehensively measured by dynamic mechanic analysis, wide-angle X-ray diffraction, and Fourier transform infrared. It is unprecedented to explore the cellulose-PAA composites as a mechanical adaptive material. The cellulose and the PAA chemically react with each other. Most of the cellulose content remains in amorphous state. Thus, the water molecules can diffuse into the composites, leading to the wetdry mechanical adaptability of the composites. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2012