Mixed-mode tensile and fatigue crack propagation studies were carried out on B4C/B fiber reinforced Ti-6A1-4V-matrix composites for the as-received, vacuum heat-treated, and air heat-treated conditions. The vacuum heat treatment had minimal effect on the tensile properties of the composite but improved the fatigue crack propagation properties. The air heat treatment degraded the fibers and the interface, resulting in loss of longitudinal strength but improvement of fatigue crack propagation properties. The fatigue crack propagation for the mixed mode 30-deg, 45-deg, and transverse specimens was self-similar. The as-received composites' mixed-mode propagation is given by (da/dN) α (ΔG/Gf)m for all the fiber orientations showing self-similar crack propagation. Humid environments accelerated the fatigue crack growth considerably compared to the vacuum and inert gas environments. Failure stress intensity (KF) appeared to have a lower value in humid environments.