Using zero-field χ AC( T) and C p ( T) (0.1 K< T <2.0 K), the magnetic properties of the Gd-sublattice in the semiconducting GdBa 2Fe 3O 8.12 was investigated. As reported earlier, though the Fe-sublattice is strongly superexchange coupled, the Gd-sublattice is paramagnetic down to 1.2 K and orders only at T N which is an order-of-magnitude lower than that of the structurally related GdBa 2Cu 3O 7− δ ( T N =2.24 K). Each of χ AC( T) and C p ( T) presents a widely broadened peak and the magnetic entropy up to 2 K attains only 30% of the value expected for a full Gd 3+ spin degeneracy. These features can be understood as follows: in contrast to the triperovskite Cu-based compound, disordering due to a random intermixing of the Ba 2+ and Gd 3+ ions induces a further weakening of the already weak Gd 3+-couplings. Finally, while the RKKY-type mechanism can be straightforwardly ruled out, the possibility of dipole–dipole or weak anisotropic superexchange couplings among the Gd-moments will be evaluated.