The effect of 20 at% Ti addition and annealing (1500 °C/100 h) on non-isothermal and isothermal oxidation behavior of as-cast hypoeutectic Nb–12Si–5Mo or hypereutectic Nb–19Si–5Mo alloys has been investigated. On heating to 1300 °C in air, the mass gain begins at lower temperature, with a steeper rise in the ternary alloys, compared to the Ti-containing alloys. On isothermal exposure for 24 h, the ternary alloys have exhibited lower mass gain at 900 °C than the quaternary alloys, but the trend has reversed at 1100 °C and 1200 °C, with the hypereutectic Ti-containing alloy exhibiting the least mass gain. The products of oxidation are found as Nb2O5 and SiO2, with TiO2, TiNb2O7 and Ti2Nb10O29 being formed additionally in the oxide scales of the Nb–12Si–5Mo–20Ti and Nb–19Si–5Mo–20Ti alloys. Analysis of the oxidation kinetics suggest an initial phase of interface-reaction controlled rapid increase of mass, followed by stage of parabolic behavior, where diffusion of O2− or Ti4+ through the oxide scale could be the rate-controlling in ternary or Ti-containing quaternary alloys, respectively. Coarser microstructure obtained by annealing has caused higher mass gain than that observed for the corresponding as cast sample. The as cast or annealed Nb–19Si–5Mo–20Ti alloy has exhibited lower values of parabolic rate constant than other alloys at ≥1100 °C, due to the formation of a defect-free oxide scale. Reduced oxygen solubility and diffusivity due to the presence of Mo and Ti in Nb-solid solution, along with formation of SiO2-rich oxide on hypereutectic quaternary alloy at 1100 °C and 1200 °C appear to be responsible for their superior oxidation resistance.