Abstract: Utilizing the techniques of Comprehensive thermal analysis and X-Ray diffraction, the thermal stability and microstructure for staple and filament of polylactic acid fibre were analyzed. The results showed that these two type of fibres have the same crystalline structure and stablity, but the staple have the higher crystallinity and melting point than filaments. The paper further measured the adsorption isotherm of C.I. Dispeses red 145 and C.I. Disperse orange 61 on the two type of fibres respectively. It was found that the adorption followed the Nernst model. the filament exhibit a stronger ability to adsorb disperse dyes, particularly for C.I. Disperse orange 64, its partition ecofficient and saturation was higher than that of staple by one time. It can be concluded that the difference in adsorption caused by the microstructure varied with the type of disperse dye. In the case of same crystalline pattern of fibre molecules, the crystal size, crystal perfection have impacts on adsorption of disperse dyes besides the main factor of the crystallinity in fibre malecules.