A cellulose-polymerized ionic liquid composite was prepared by in-situ polymerization method using two kinds of ionic liquids, which dissolved cellulose as a solvent and had a polymerizable acrylate group, respectively. Cellulose was dissolved in the ionic liquid of the solvent, and the radical polymerization of the polymerizable ionic liquid was carried out by 2,2′-azobis (isobutyroniitrile) in the solution. The results of the IR spectrum and elemental analysis indicated that the isolated product was a composite consisting of cellulose and the polymerized ionic liquid. The TG and DSC data of the product were different from those of cellulose, supporting the efficient compatibilization of cellulose with the polymerized ionic liquid in the composite.