Molecular weight determination of 83% degree of deacetylation (DD) chitosan with non-Gaussian and broad molecular weight distribution by high-performance size exclusion chromatography (HPSEC) and by capillary viscometry were proposed. The relationships between weight average retention volumes (RVw) of HPSEC and intrinsic viscosities ([eta]) measured by capillary viscometer and the weight average molecular weight (Mw) measured by static Light scattering were established for routine molecular weight determination of chitosans either by HPSEC or by the capillary viscometry method, respectively. These results showed: relationships of RVw and Mw for different Mw of 83.0% DD chitosans can be expressed by the equation Log Mw = -0.439 RVw + 11.66. The RVw of other DD chitosans do not correlate well with this equation. It indicated that DD of chitosan affected the relationship of RVw and Mw of chitosans studied. The Mark-Houwink constant a decreased from 0.715 to 0.521, as the solution ionic strength increased from 0.01M to 0.30M, whereas constant k increased from 5.48 x 10(-4) to 2.04 x 10(-3) over the same range of ionic strength solutions. The established RVw and Mw equation and [eta] and Mw equation (Mark-Houwink equation) can be routinely used to determine the molecular weight from RVw or [eta] of chitosan by HPSEC or by capillary viscometer, respectively, without the need of expensive instrumentation.