The samples of chitosan with different degree of deacetylation and the molecular weight range of 1.3～15.1×105 were prepared and characterized by FTIR and viscosity measurements. The phase transition and states of the lyotropic liquid crystals of chitosan in dichloroacetic acid were studied by polarized microscopy. It was shown that the critical concentration for the formation of the liquid crystals decreases slightly as molecular weight of chitosan increases in the range of 105～106. It was found that the effect of the deacetylation degree in the range of 70%～90% on the critical concentration could be neglected.l The experimental values of the critical concentration were in agreement with the calculated ones based on the Khokhlov-Semenov-Odijik theory

which indicated that the lyotropic behavior of chitosan in dichloroacetic acid can be well described with wormlike chain model.