Temperature and magnetic field dependencies of the magnetization of single crystal Gd5Ge4 indicate antiferromagnetic coupling along the c direction below 130 K. Both a reversible spin-flop transition when a magnetic field of ∼8.4kOe is applied along the cdirection, and irreversible metamagneticlike transitions when a 20 kOe or greater magnetic field is applied at 4.3 K along any of the three crystallographic axes are observed. Although Gd3+ ions have negligible single ion anisotropy, the metamagnetic transitions and magnetization of Gd5Ge4 in the ferromagnetic state depend on the crystallographic direction reflecting the anisotropy of the exchange interactions due to the distinctly layered Sm5Ge4-type crystal structure.