Novel blends from quatemized polysulfone (QPSF) and benzoyl guar gum (BGG) coded as QB with different contents (10-80 wt%) were prepared through solution casting method. Simultaneously, other kinds of blends were prepared from chloromethylated polysulfone (CIPSF) and BGG coded as CIB to compare the effects of the substituted groups on the miscibility and proper-ties of the composite materials. The effect of BGG content on QB blends was investigated by Fourier transform infrared spectroscopy (FIFIR), scanning electron microscopy (SEM), atom force microscopy (AFM), differential scanning calofimetry (DSC) and tensile tests. The results revealed that QB blends had good or certain miscibility over the entire composition ratio of BGG to QPSF under study. Compared with ClB blends, QB blends exhibited stronger interfacial attraction and better phase mixing as a result of the relatively strong hydrogen bonding and the specific electrostatic interaction between QPSF and BGG. The occurrence of strong interaction between QPSF and BGG played a key role in improving the material performance. With an increase of BGG content in the blends, the tensile strength of QB blends increased from 33.1 to 44.3 MPa. Furthermore, the mechanical properties of QB-20 blend at different RH were also discussed. It was found that the composite properties changed considerably with moisture content. which attributed that water molecules had a great effect on the hydrogen bonding between the two polymers. (c) 2006 Elsevier Ltd. All rights reserved.