  While pyrite-type PtBi2 with face-centered cubic structure has been predicted
to be a three-dimensional (3D) Dirac semimetal, experimental study on its
physical properties remains absent. Here we report the angular-dependent
magnetoresistance (MR) measurements of PtBi2 single-crystal under high magnetic
fields. We observed extreme large unsaturated magnetoresistance (XMR) up to
11.2 million percent at T = 1.8 K in a magnetic field of 33 T, which surpasses
the previously reported Dirac materials, such as WTe2, LaSb and NbP. The
crystals exhibit an ultrahigh mobility and significant Shubnikov-de Hass (SdH)
quantum oscillations with nontrivial Berry's phase. Analysis of Hall
resistivity indicates that the XMR can be ascribed to the nearly compensated
electron and hole. Our experimental results associated with the ab initio
calculations suggest that pyrite PtBi2 is a topological semimetal candidate
which might provide a platform for exploring topological materials with XMR in
noble metal alloys.
