Variation of weight average molecular weight ($ar{M}_{w}$) with processing temperature and time elapsed in acetic solution of chitosan was investigated by high performance liquid chromatography(HPLC), rotary viscometer, and capillary viscometer. The molecular weight distribution on chromatographs suggested that molecular chains of chitosan were degraded continuously by acid hydrolysis in aqueous acetic solution. The $ar{M}_{w}$, degree of deacetylation, apparent viscosity, and intrinsic viscosity decreased with increasing temperature and time in 2 wt$\%$ acetic solution. The $ar{M}_{w}$ decreased rapidly with increasing temperature above $30^{circ}C$, and decreased to less than $25\%$ within initial 12 hours at $50^{circ}C$. Above $ar{M}_{w};9.2 imes10^{4}$, the apparent viscosity showed a linearly propertional relationship to $ar{M}_{w}$. The intrinsic viscosity was determined in 0.1 M acetic acid/0.2 M sodium chloride solution in order to compare with $ar{M}_{w}$. Gross solution conformation factor a in the Mark-Houwink equation suggests that chitosan molecular chains assume coil conformation in dilute acetic solution.