Hemp fibers were used as natural reinforcement in composites of thermosetting vegetal oil based resin. Boards with fibers content from 0 to 65 vol % were produced by hot pressing. The mechanical properties were investigated with flexural testing. The effect of effect has been observed on both modulus and strength, indicating a good fiber-matrix interfacial adhesion, which was confirmed by means of scanning electron microscopy observations. Dynamic mechanical analysis also showed an important reinforcement effect in the polymer rubbery region, where at 180 degrees C the storage modulus increased from 17 MPa for the neat resin to 850 MPa for 65 vol % fiber content composites. It also revealed an glass transition temperature decrease when fiber amount in the composite increased. Additional experiments based on differential scanning calorimetry show a weakly accelerated cure when fibers content increases, which usually lead to a lower T-g. But, this phenomenon alone cannot explain the observed T-g change. Contact angle on hemp evolution with time for the resin components show that anhydride is totally absorbed after a few seconds, whereas contact angle of epoxydized oil decreases slowly. This indicates probably a preferential anhydride absorption that leads to a lower amount of anhydride in the matrix and as a consequence to a reduced T-g. (c) 2006 Wiley Periodicals, Inc.