An easy and environmentally friendly strategy is shown for the synthesis of dialdehyde cellulose/silver nanoparticle composites using dialdehyde cellulose as reducing agent through the microwave-assisted hydrothermal method. The effects of the microwave heating time and temperature on the products were investigated by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), and thermogravimetric analysis (TGA). The dialdehyde cellulose was found to be an efficient reducing agent for silver ions, and the microwave heating time and temperature played a vital role in the morphologies of the silver nanostructures. The influences of different additional reductants such as ascorbic acid and glucose on the shapes, size-distribution, phase, and crystallinity of the samples were comparatively investigated in detail. This strategy is environmentally friendly, surfactant-free, without any other reducing or stabilizing agent chemicals, and the as-prepared dialdehyde cellulose/silver nanoparticles were more convenient to use in biomedical fields.