  We have used the de Hass-van Alphen (dHvA) effect to investigate the Fermi
surface of high-quality crystalline TiSb2, which unveiled a nontrivial
topologic nature by analyzing the dHvA quantum oscillations. Moreover, our
analysis on the quantum oscillation frequencies associated with nonzero Berry
phase when the magnetic field is parallel to both of the ab-plane and c-axis of
TiSb2 finds that the Fermi surface topology has a three-dimensional (3D)
feature. The results are supported by the first-principle calculations which
revealed a symmetry-protected Dirac point appeared along the {\Gamma}-Z high
symmetry line near the Fermi level. On the (001) surface, the bulk Dirac points
are found to project onto the -{\Gamma} point with nontrivial surface states.
Our finding will substantially enrich the family of 3D Dirac semimetals which
are useful for topological applications.
