The phase relations in the ternary system Yb–Zn–Ga have been studied at 400 °C for the partial isothermal section in the 0–33.3 at.% ytterbium concentration range. X-ray powder diffraction (XRPD), optical microscopy (OM) and scanning electron microscopy (SEM), complemented with energy dispersive X-ray spectroscopy (EDS), were used to analyse the microstructures, identify the phases and characterize their crystal structures and compositions. The Yb–Zn–Ga partial section at 400 °C is characterized by the presence of an extended solid solution, YbZn2−xGax (0≤ x ≤ 1), and the existence of four ternary intermetallic compounds, YbZnxGa4−x, 0.75≤ x ≤ 2 (BaAl4-type), YbZnxGa4−x, 0.25≤ x ≤ 0.5 (CaCu0.15Ga3.85-type), Yb3Zn11−xGax, 3.5≤ x ≤ 4.2 (La3Al11-type) and YbZn11−xGax, 1.8≤ x ≤ 2.7 (BaHg11-type), the last three being reported here for the first time. Sixteen ternary phase fields have been identified in the studied partial isothermal section at 400 °C.