High alpha-cellulose has been dissolved in two non-degrading solvent systems like dimethyl sulfoxide/paraformaldehyde (DMSO/PF) and N,N-dimethyl acetamide/lithium chloride (DMAc/LiCl) and then fractionated to different molecular weight fractions by regeneration technique. Esters of the different molecular weight fractions of cellulose have been prepared having substitution chain length of C-2-C-5 using pyridine as catalyst. The esters are characterized by IR and H-1-NMR spectroscopy. Thermal characterization of the esters is done by thermogravimetric and differential thermogravimetric analysis and the kinetic parameters of thermal degradation are measured by using Coats and Redfern equation. It is found that the temperature of active decomposition decreases with the increase in substitution chain length and also with the decrease in molecular weight of the fractions. The mechanism of thermal degradation has also been studied. Cellulose acetate prepared in DMSO/PF solvent system shows higher temperature of active decomposition (367.5 degrees C) than that prepared in DMAc/LiCl solvent system (350 degrees C). This is due to the formation of methylol cellulose ester in DMSO/PF solvent system.