Water-induced mechanically adaptive rubber nanocomposites were prepared by mixing bacterial cellulose whiskers (BCWs) suspension with carboxylated acerlonitrile-butadiene rubber (XNBR) latex, followed by latex blending method. The introduction of BCWs into XNBR enhanced the tensile storage modulus (E') significantly, which originated from the formation of a rigid 3D filler network within matrix as well as the interfacial interaction between filler and matrix. The water uptake ratio of nanocomposite films increased with BCWs content, from 5.5% for neat XNBR to 54% for nanocomposite with 20 phr (parts per hundred rubber) BCWs. Upon submersed in water, the nanocomposite films showed dramatic decrease in E ', especially for which filled with high BCWs loadings. For example, E ' of nanocomposite with 20 phr BCWs was decreased by 98.04% after equilibrium swelling compared with only 52.02% for nanocomposite with 3 phr BCWs. The remarkable water-triggered modulus changes are attributed to the disentanglement of BCWs network after swelling. The prepared XNBR-BCWs nanocomposites with mechanically adaptive properties could contribute to develop the new type of rubber-based smart materials. POLYM. ENG. SCI., 59:58-65, 2019. (c) 2018 Society of Plastics Engineers