WC-10%Co alloy and two series of WC-TiC-10%Co alloys with 0.64 and 1.28%TiC, having various carbon contents in the phase range free from the η and graphite phase, were vacuum-sintered mainly at 1375°C for 1.5 hr. Effects of the TiC addition to the sintered WC-10%Co alloys on their properties and, moreover, on their binder phase were studied, in details by measuring their density, lattice constant of the binder phase, relative magnetic saturation, hardness, transverse-rupture strength, grain size of WC, etc..The experimental results obtained are as follows. (1) The variation of general properties of the TiC containing alloys, due to a small change of the carbon content, is equal to that of straight WC-Co alloys(2)(4) as reported previously. (2) The value of magnetic saturation of the alloys and the lattice constant of the binder phase which are changeable according to their carbon content are also identical with the straight alloys. From this and the formation of the WC-TiC solid solution by the 0.15%TiC addition, it may be concluded that TiC is hardly soluble in the binder phase. In this respect, the behaivior of TiC is almost similar to that of TaC. (3) The width of the γ+ carbides range and the position of the stoichiometric carbon content in that range are in good agreement with those of the straight alloys. (4) It can be predicted that the addition of a small amount of TiC to the WC-Co alloys inhibits the recrystallization of the carbide phase, and consequently the alloys have finer WC grains and higher hardness than the corresponding alloys of TiC free compositions. Because of this finer structure, the rate of precipitation of the Co3W type compound from the binder phase is accelerated when the low carbon alloys are annealed at low temperatures. (5) The TiC addition makes the η-phase grain finer and improves its dispersion, so that the strength of the alloys even under the appearance of then phase dces not decrease abruptly.