Two polyoxometalate-based host-guest compounds, (HL₁)₂(HPW₁₂O₄₀)·~11H₂O (1), (HL₂)₃(PW₁₂O₄₀)·3H₂O (2) (L₁ = guanine, L₂ = 2-(1H-1,2,4-triazol-3-yl)pyridine), were synthesized under hydrothermal conditions and characterized by EA, PXRD, TG, FT-IR and X-ray single-crystal diffraction. Compound 1 crystallizes in trigonal space group P-3 with a = 18.2917(5), b = 18.2917(5), c = 13.5441(5) Å, V = 3924.5(3) ų, Z = 3, M_r = 3383.26 g/mol, ρ_calc = 4.036 g/cm³, F(000) = 4137, μ = 48.532 mm^–1, GOOF = 1.062, the final R = 0.0713 and wR = 0.1865 for 9037 observed reflections with I > 2σ(I). Compound 2 crystallizes in trigonal space group R-3 with a = 19.0017(6), b = 19.0017(6), c = 25.6361(9) Å, V = 8016.2(6) ų, Z = 6, M_r = 3372.45 g/mol, ρ_calc = 4.188 g/cm, F(000) = 8886, μ = 47.644 mm^–1, GOOF = 1.077, the final R = 0.0380 and wR = 0.0976 for 5904 observed reflections with I > 2σ(I). These two compounds can catalyze selective oxidation of aniline with H₂O₂ as the oxidant. Under optimal conditions, the conversion of aniline with compound 1 can reach up to 91.25%, and the selectivity of nitrosobenzene is 78.81%.