We found that the pseudo binary alloys Mn1-xRux3Ga, with 0.33≤x≤0.67, have an ordered b.c.c. structure. The lattice constant a is almost constant with respect to x: a=6.000 Å for x=0.33 and a=5.992 Å for x=0.67. For the alloy with x=0.33, i.e. Mn2RuGa, the magnetization is almost saturated in a field of 20 kOe. The saturation magnetization at 4.2 K is 23 emu/g, and the Curie temperature, TC, is 460 K. The TC of (Mn1-xRux)3Ga decreases almost linearly with increasing x, and it vanishes around x=0.67 (MnRu2Ga). We also determined atomic and magnetic structures from neutron diffraction experiments. The alloy Mn2RuGa (x=0.33) has an ordered structure of CuHg2Ti type; the magnetic Mn atoms mainly occupy the 4a (0,0,0) and 4d \(\frac\Box3\Box\Box4\Box\),\(\frac\Box3\Box\Box4\Box\),\(\frac\Box3\Box\Box4\Box\) sites. We also observedthat the magnetic moments of Mn atoms on the 4a and 4d sites are antiparallel to each other; values of the magnetic moment are μa=4.6 and μd=3.3 μB per Mn atom.