An investigation is reported of the effects of three different coatings onto diamonds in the composites for the beads of wire saws. The matrix of the composites contained 80% (w/w) cobalt. Ti, W, and W-Co were coated onto diamond surfaces respectively and then incorporated into the matrix. The mixed powders were hot-pressed to form the specimens for bending tests. Coupled with the results of bending tests and the strength of coated diamonds, the coatings of W were found to be best among the three coatings. Further experiments indicated that the thickness of W-coatings onto the diamonds should be controlled around 10(m in order to obtain an excellent retention of diamonds.