Dense WC-base W-C-B composites were prepared by the reaction sintering of B4C-W-WC (mole ratio 1 : x : 80 or 130, x = 1-9) powder mixtures using resistance-heated hot pressing. Sintered bodies were composed of different products depending on x both in B4C-xW-80WC and -130WC: WC + WB when xless than or equal to 3, WC +W2B + WB when x = 5, and WC + W2B + W2C when xgreater than or equal to 7. They had the highest Young's modulus values 706 and 705 GPa for -80WC and -130WC at x= 3, respectively. The hardness was increased with x, depending on a decrease in the grain size of WC. Its highest value was 24.5 GPa both for -80WC and -130WC at x = 9. For the fracture toughness, the highest value 6.1 MPa m(1/2) was obtained for -130WC at x = 5.