The dissolution process and dissolved state of cellulose into a dimethylformamide-chloral-pyridine (D-C-P) system were studied by optical microscopy, nuclear magnetic resonance (NMR), polarimetry, infrared (IR) spectroscopy, and X-ray diffraction method. Natural cellulose with crystal form I dissolves rapidly at room temperature, via hemiacetaltype reaction with chloral, in which pyridine acts as a reaction accelerator. Cellulose exists as cellulose trichlorate in the mixture. When the pretreatment period of cellulose with dimethylformamide (DMF) is short, the cellulose dissolves into the system without swelling. But when the pretreatment period is relatively long, the cellulose swells considerably and then dissolves. Cellulose monochlorate was recovered by casting from the solution but cellulose trichlorate could not be isolated, probably because of the considerable tendency of the polymer to hydrolyze, especially when the solution is acidic. Cellulose having the crystal form II was regenerated by addition of water to the solution. KEY WORDS Cellulose Chlorate I Dissolution Process I Dissolved State I Dimethylformamide-Chloral-Pyridine System I