Two hexameric chromium–lanthanide heterometallic cluster substituted polyoxometalates (POMs), K₉Na₁₄Cs₁₂H[Cr₆Dy₆(H₂O)₁₂(α-GeW₁₀O₃₈)₆]·33H₂O (1-Dy) and K₉Na₁₄Cs₁₂H[Cr₆Tb₆(H₂O)₁₂(α-GeW₁₀O₃₈)₆]·65H₂O (1-Tb), have been hydrothermally synthesized and structurally characterized through single-crystal X-ray diffraction analysis, powder X-ray diffraction analysis, thermogravimetric analysis, infrared spectroscopy and solid-state ultraviolet-visible spectroscopy. Compounds 1-Dy and 1-Tb represent the first examples of 3d–4f heterometallic cluster substituted POMs incorporating chromium–lanthanide clusters. What's more, magnetic investigations indicate that overall antiferromagnetic coupling is present in 1-Dy and 1-Tb.