This thesis presented a complete measurement method for accurate characterization of balanced devices using two-port vector network analyzer. Combining renormalization and mixed-mode transformation techniques, this method is good for coaxial components. At first, the feasibility of the method was confirmed with the help of ADS simulation. Then a real example of Marchand balun fabricated on FR4 substrate was measured with calibrated mixed-mode S-parameters that have been further verified by full-wave simulations. The measurement system developed based on this method does not require any additional hardware to the vector network analyzer. This system can be also applied to the measurement of on-wafer components with the help of some microwave switches.