Porous formation and supermolecular structure of regenerated cellulose (RC) microporous membranes prepared by coagulating mixture solution of cellulose cuoxam and polyethylene glycol (PEG400, PEG2000, PEG6000 and PEG20000) were investigated. SEM showed that the cellulose cuoxam/PEG mixture solution formed a homogeneous blend, and the miscibility between cellulose and PEG decreased with increasing molecular weight (M-w) of PEG. The mixture solutions exhibited homogeneous particles in aqueous 10 wt.% NaOH solution, and a smooth surface of RC membrane was observed after immersing in 5 wt.% H2SO4, suggesting that a new molecular architecture of cellulose is formed during the H2SO4 coagulation process. With an increase in M-w of PEG, crystallinity chi(c) slightly decreased, while (1 (1) over bar 0) plane orientation parameter f(//)(1 (1) over bar 0) of the membranes increased. The C-13 CP/MAS NMR spectra indicated that the PEG molecules as pore former were completely removed from the membranes mixed with PEG400, while only 4 wt.% PEG remained in the membranes mixed with PEG2000, PEG6000 and PEG20000. The results of a spin-lattice relaxation suggested that intramolecular hydrogen bonds of cellulose molecules in the membranes decreased, and inter-molecular hydrogen bonds increased, when M-w of PEG increased. M-w of PEG plays an important role in the morphology, structure and the pore size of the microporous cellulose membranes.