We have developed the first direct, organo-catalytic, bulk ring-opening polymerization (ROP) of epsilon-caprolactone (epsilon-CL) with solid cotton and paper cellulose as the initiators. The mild ROPs were performed without solvent, and are operationally simple, inexpensive and environmentally benign. Organic-acid-catalyzed heterogenous derivatization of cellulose provides a novel route to valuable cellulose-based biocompatible nanomaterials. The furnished polymerization products were characterized by FTIR, H-1 and C-13 NMR spectroscopy, MALDI-TOF mass spectrometry and electron microscopy.