Abstract We have investigated the magnetic structures and phase transitions of PrMn 2− x Fe x Ge 2 (0 ≤ x ≤ 1) by the temperature dependence of weak-field magnetization and powder neutron diffraction. For the x = 0.6 sample, a typical SmMn 2Ge 2-like magnetic behavior is observed. The magnetic structures of the samples with x = 0.6, 0.8 and 1 have been determined between 1.5 and 305 K. Above T C inter ( x = 0.6) and T N inter ( x = 0.8 and 1) up to T N inter , these samples exhibit an intralayer antiferromagnetic structure in (0 0 1) Mn planes. For x = 0.6 sample, the magnetic structure is canted ferromagnetic along the c-axis between T N inter and T C inter and below T C Pr . For the samples with x = 0.8 and 1, the magnetic structure is canted antiferromagnetic along the c-axis below T N inter . Pr moments order ferromagnetically along the c-axis for the x = 0.6 sample below T C Pr . The results are summarized in the PrMn 2− x Fe x Ge 2 magnetic phase diagram. The general magnetic phase diagram for RMn 2− x Fe x Ge 2 (R: La, Ce, Pr, Nd and Sm) is also constructed from previous and present works. For these compounds, the magnetic phase transition from ferromagnetic to antiferromagnetic occurs at different intralayer Mn–Mn distances for each system. These critical distances are larger than the corresponding threshold value d Mn – Mn a = 2.87 Å for the ternary end-member RMn 2X 2 compounds.