In an earlier study, it was found that Ti-7.5Mo-1Fe and Ti-7.5Mo-2Fe alloys exhibited markedly different mechanical properties. While Ti-7.5Mo-2Fe alloy exhibited excellent mechanical properties, Ti-7.5Mo-1Fe alloy showed an extremely brittle behavior. The present study is a continual research on these two particular alloys with a focus on the effect of omega phase on the deformation behavior of the alloys. The results indicate that 2Fe alloy exhibited a ductile type fracture surface covered with normal deformation dimples. The fracture surface of 1Fe alloy exhibited a terrace-like morphology with numerous sub-micron-sized dimples. Throughout the entire plastically deformed region of 1Fe alloy, {112} (111) type twins were observed, but few twins formed in 2Fe alloy. It is suggested that the numerous, larger-sized W particles in 1Fe alloy have effectively restricted the slip of dislocations that largely limited plastic deformation capability of the alloy. The less and smaller w particles could not do the same to 2Fe that led to the observed ductile behavior. (C) 2002 Published by Elsevier Science B.V.