The fibre of Grewia  bicolor bark (GB) was extracted and used as reinforcement for the development fibreboards using orthophtalique unsaturated polyester (UP) as a matrix. Two methods of extraction of fibres were used, namely biological retting and chemical extraction by a sodium hydroxide solution at a 5% concentration. Chemical, Physical, mechanical, and thermal  characteristics  were  determined  using  ATF  FTIR,  mechanical  test  and thermogravimetric analysis. The theoretical density of the characterized fibres was 1.30 g/cm3. The porosity decreases by 5% from the root to the leaves. The SEM analysis indicated the presence of fibrils coated with a rough sheath similar to a honeycomb cell structure. The use of NaOH in the extraction method removes the hemicellulose, pectin, wax, and lignin from the fibres. The average elasticity modulus of untreated and treated fibres are, respectively, E = 35.18 ± 2.25 MPa and E = 33.47 ± 2.35 MPa and internal bond of fibreboards are 0.98 ± 0.05 MPa and 1.06 ± 0.02 MPa.