Pot soil was supplemented with varying concentration of chitin or chitosan to investigate their influence on the nodulation, nitorgen fixation and growth of soybean plants. Significant (P=0.05) reductions in nodule fresh weight and nitrogen fixaton (measured as acetylene-reduction activity) were observed at the early growth stage (28 DAP) for plants grown in soil supplemented with chitin or chitosan as compared to regular pot soil. However, the nodule numbers were not affected at the early growth stage with the exception of 1% of chitin or chitosan. Both nodulation and nitorgen fixation activity at a later growth stage (42 DAP) were markedly enhanced in soils supplemented with 0.10% of either chitin or chitosan. These results suggest that all concentrations of chitin or chitosan have a severe influence on nodule development and N2-fixation activity at the early growth stage in soybean plants. The production of total dry matter was higher in untreated control plants at 28 DAP, while plants treated with 0.10∼0.25% chitin or chitosan produced higher dry matter at 42 DAP. Soybean seed yield increased with the increasing pod number at these levels of treatment. However, the above parameters did not differ greatly between chitin and chitosan at corresponding levels of concentration.