Abstract: The biodegradable composites made f rom bagasse fibre and biodegraded resin were prepared by pressforming , and the effect s of alkali t reatment s on the fibres and composites were investigated. Compared with 3 % and5 % alkali solution , the composites reinforced with 1 % alkali solution t reated fibre show maximum improvement inmechanical properties. Af ter alkali t reatment , the fibrillation occurs and the surface of the fibres get s finer , whichcont ributes to the improvement of fibre2mat rix adhesion , and result s in enhancing the mechanical properties of composites. Furthermore , the increase of st rength and aspect ratio and the reduction of defect concent ration in the t reated fibres also improve the properties. In comparison with the unt reated composites , approximately 13 % improvement in tensile st rength , 14 % in flexural st rength and 30 % in impact st rength have been found , respectively. SEMobservations on the f racture surface of the composites show that the fibre-mat rix adhesion is improved af ter alkalit reatment s.