  EuSn2As2 with layered rhombohedral crystal structure is proposed to be a
candidate of intrinsic antiferromagnetic (AFM) topological insulator. Here, we
have investigated systematic magnetoresistance (MR) and magnetization
measurements on the high quality EuSn2As2 single crystal with the magnetic
field both parallel and perpendicular to (00l) plane. Both the kink of magnetic
susceptibility and longitudinal resistivity reveal that EuSn2An2 undergoes an
AFM transition at TN = 21 K. At T = 2 K, the magnetization exhibits two
successive plateaus of ~ 5.6 {\mu}B/Eu and ~ 6.6 {\mu}B/Eu at the corresponding
critical magnetic fields. Combined with the negative longitudinal MR and
abnormal Hall resistance, we demonstrate that EuSn2An2 undergoes complicated
magnetic transitions from an AFM state to a canted ferromagnetic (FM) state at
Hc and then to a polarized FM state at Hs as the magnetic field increase.
