The discharge coefficients of the sonic Venturi nozzle were measured for eleven gases on the Reynolds number range from 2×10³ to 4×10⁴. The results showed that the discharge coefficients strongly depend on gases. And it was also suggested that the discharge coefficients of most of the gases tested can be described by using two parameters theoretically determined on the assumption of isentropic flow of ideal gas, if they are on the conditions which are not so far from the ideal gas state. The differences between the theoretical and the experimental discharge coefficients were within 0.5 percent, except for CO₂, SF₆ and C₃H₈.