Tensile properties and fine structure of ramie cellulose IIII obtained with either ethylenediamine or liquid ammonia were compared. The fibre treated with ethylenediamine had lower crystallinity index, elastic modulus and tensile strength, and greater internal surface area and strain-at-break than the fibre treated with liquid ammonia. The load-elongation behaviour of the fibres was interpreted by using a two-phase parallel-series mechanical model comprising two types of springs representing the crystalline and amorphous components to give a single value of the elastic constant for the cellulose III crystal. The analysis gave sets of model parameters, revealing a remarkable difference in the mechanical contribution of crystal and amorphous components in the two samples. Calculation based on these results gave an elastic modulus of 115-122 GPa for the cellulose III crystallite, and 4.6-8.2 and 9.6-10 GPa for the amorphous components in ethylenediamine and liquid ammonia-treated fibres, respectively.