Composites mimicking the plant-cell wall structure were prepared by synthesizing deuterated bacterial cellulose in D-based culture medium including hemicelluloses from wood. The partial intracrystalline deuteration of bacterial cellulose was demonstrated by FT-IR spectra, which also showed that the hemicelluloses modified the cellulose crystal structure in both the water-accessible and water-inaccessible parts of the fibrils. The hierarchical wet-state structure of the composites was characterized using small-angle neutron scattering (SANS) and the cross-sectional fibril dimensions were compared to scanning electron microscopy images of freeze-dried samples and earlier small-angle X-ray scattering results from hydrogenated samples. The SANS data of deuterated bacterial cellulose/hemicellulose composites revealed a decrease of the microfibril cross-section and looser packing of the microfibrils into wider bundles in the presence of hemicelluloses.