An in situ (TiB + TiC)/Ti-1100 composite was prepared by reacting B4C and Ti. The effect of the amount of deformation during thermomechanical processing (TMP) on the microstructure, orientation of TiB whiskers, and the mechanical properties of the composite were investigated. Improvements in the composite tensile strength from TMP are discussed in terms of grain refinement and TiB whisker rotation. A model is suggested to predict the TiB whisker orientation factor for the composite after TMP with various amounts of deformation. Based on the effect of grain refinement and rotation of the TiB whiskers, the yield strengths of the composite after TMP with various amounts of deformation were modeled. The modeled values agreed well with the test results.