The preparation and functionalization of cellulose microgels (CMGs) has been presented. Only a trace concentration of CMGs (< 0.2 wt.%) stabilized oil-in-water (O/W) emulsions and produced high internal phase emulsions (HIPE). The size and morphology of the CMGs were characterized with dynamic light scattering (DLS) and atomic force microscopy (AFM), and the structural properties were discussed. Based on the experimental results,the correlation between the amphiphilicity, and adsorption of the CMGs, and their capability to stabilize the emulsions, which are closely related to the cross-linking density of the CMGs, were elaborated. Having a porous percolating structure and being rich in free hydroxyl groups, the CMGs were functionalized by Fe3O4. The unique dispersibility of the Fe3O4-CMGs and their ability to stabilize the emulsions were investigated in detail. The results pave the way to a deeper understanding of Pickering emulsions stabilized by soft solvent-swollen materials and are expected to further expand the application of cellulose.