Microstructure evolution and its influence on the mechanical properties of (Ti 65.5 Fe 34.5 ) 100Àx Nb x (x ¼ 0, 3, 5 and 7) ultrafine composites has been investigated. The Nb-containing alloys exhibit simultaneously improved compressive mechanical properties, i.e. high yield (1.9-2.2 GPa) and fracture (2.2-2.6 GPa) strength together with large plasticity (6-13%), due to a favorable modulation of their ultrafine eutectic microstructure. The enhanced mechanical properties are strongly related to the lengthscale, volume fraction and distribution of proeutectic phase as well as to the refinement and interphase coherency of the alternating ultrafine eutectic layers.