Tungstovanadosilicic heteropoly acid H5SiW11VO40·15H2O has been successfully synthesized and characterized. The single crystal of this solid proton conductor was firstly obtained and the crystal structure was determined from single crystal X-ray diffraction. The complex crystallizes in the monoclinic system, space group C2/c, with a = 12.716(3) Å, b = 19.881(5) Å, c = 19.099(5) Å, α = 90°, β = 90.796°, γ = 90°, V = 4828(2) Å, Z = 4. Its proton conductivity was measured using electrochemical impedance spectroscopy (EIS) in the temperature range 15–55 °C, and the activation energy of the conductivity was determined. The results show that it has appreciable proton conductivity (7.93 × 10−3 S cm−1) at 15 °C and 50% relative humidity, with an activation energy of 21.59 kJ mol−1 for proton conduction. The conductive mechanism is Vehicle mechanism.