The naturally occurring Guar gum (GG) was chemically modified with polyaniline (PANI) using ammonium persulfate (APS) as oxidant/initiator in acidic condition. The representative graft copolymer was characterized using UV-vis, FTIR, H-1 NMR, XRD, TGA, and SEM taking GG and PANI as reference. The affinity of the upper limit for the graft copolymerization has been extensively studied by varying different chemical and physical parameters. All the findings have been discussed, and proposed a plausible mechanism for the graft copolymerization. The grafted GG exhibited hybrid properties of biopoly- mer as well as PANI, and has electrical conductivity in the range of 1.6 X 10(-2) S/cm at room temperature. The electrical conductivity of the grafted biomaterial was quite sensitive with pH, and it could be interesting to combine a biopolymer, isolated from the natural resources with synthetic polymer from petrochemical origin, and yielded an eco-friendly material of high performance. (C) 2008 Wiley Periodicals, Inc.