  Temperature and field-dependent magnetization $M(H,T)$ measurements and
neutron scattering study of a single crystal CeSb$_2$ are presented. Several
anomalies in the magnetization curves have been confirmed at low magnetic
field, i.e., 15.6 K, 12 K, and 9.8 K. These three transitions are all
metamagnetic transitions (MMT), which shift to lower temperatures as the
magnetic field increases. The anomaly at 15.6 K has been suggested as
paramagnetic (PM) to ferromagnetic (FM) phase transition. The anomaly located
at around 12 K is antiferromagnetic-like transition, and this turning point
will clearly split into two when the magnetic field $H\geq0.2$ T. Neutron
scattering study reveals that the low temperature ground state of CeSb$_2$
orders antiferromagnetically with commensurate propagation wave vectors
$\textbf{k}=(-1,\pm1/6,0)$ and $\textbf{k}=(\pm1/6,-1,0)$, with N\'eel
temperature $T_N\sim9.8$ K. This transition is of first-order, as shown in the
hysteresis loop observed by the field cooled cooling (FCC) and field cooled
warming (FCW) processes.
