The LuMn 6Ge 6− x Ga x compounds ( x=0.4, 0.7, 1.0) were studied by magnetization measurements and neutron diffraction. The LuMn 6Ge 5Ga compound is ferromagnetic in its whole ordered range ( T c=352 K). The Mn moments (2.02(8) μ B at 2 K) are close to the (001) plane. The LuMn 6Ge 5.3Ga 0.7 compound displays a Néel point at 372 K and is helimagnetic in the whole temperature range investigated by neutron diffraction (2–300 K). At 2 K, the normal to the helical plane makes an angle of 45(1)° with the c-axis, and the moment is refined to μ Mn=2.36(5) μ B. The LuMn 6Ge 5.6Ga 0.4 compound displays a Néel point at 451 K. Neutron diffraction indicates that, above T t∼290 K, the compound is colinear antiferromagnetic, as characterized by a doubling of the c-axis and with a moment direction parallel to the c-axis. Below T t′∼230 K, the compound becomes helimagnetic. At 2 K, the normal to the helical plane makes an angle of 42(1)° with the c-axis, and the moment is refined to μ Mn=2.24(4) μ B. The corresponding q z component of the propagating vector [0.2082(4)] at 2 K is significantly different from that measured in the LuMn 6Ge 5.6Ga 0.4 compound [0.1067(6)]. The effects of Ge substitution on the magnetic properties are discussed.