The magnetic properties of Tb 4 Sb 2 Bi, Tb 4 Sb 2.75 Ge 0.25 and Tb 4 Sb 2.3 Si 0.7 solid solutions (Th 3 P 4 -type, cubic; cI28, space group I4¯3d, No. 220) have been investigated by means of magnetization and neutron diffraction studies. The magnetization measurements indicate that the Tb 4 Sb 2 Bi compound orders magnetically at 120K (T N ) and 50K (T C ). The magnetization vs. field isotherm at 5K shows signature of ferromagnetic order. Neutron diffraction experiment in zero applied magnetic field shows that below T N =125(4)K Tb 4 Sb 2 Bi exhibits a antiferromagnetic flat spiral type ordering with wave vector K 1 =[±K X ,±K X ,±K X ] (K X value changes from 0.1033 up to 0.158 in the temperature interval down to 2K). Below T m =70(4)K the decreasing of antiferromagnetic component coincides with increasing of the ferromagnetic component and about T CN =55(4)K, Tb 4 Sb 2 Bi shows ferromagnetic transition. At 2K, the magnetic structure of Tb 4 Sb 2 Bi is ferromagnetic cone and the cone axis is along [111] direction.Neutron diffraction study of Tb 4 Sb 2.75 Ge 0.25 indicate an antiferromagnetic ordering at 155(4)K (ferromagnetic cone with K 1 =[±0.136(2), ±0.136(2), ±0.136(2)]) and ferromagnetic ordering (sharp increasing of ferromagnetic component) at 145(4)K. The K X value is nearly constant from 155K down to 2K. At 2K, the magnetic structure of Tb 4 Sb 2.75 Ge 0.25 is ferromagnetic cone with a weak antiferromagnetic component and the cone axis is along [111] direction.Low field magnetisation measurements on Tb 4 Sb 2.3 Si 0.7 indicate a ferromagnetic ordering at T C ∼180K. Thus small substitutions of Bi, Ge and Si at Sb-site of Tb 4 Sb 3 are found to increase the magnetic ordering temperature of the parent compound.