It is proposed and demonstrated that the fiber-optic Mach-Zehnder (MZ) interferometry can measure accurately the elector-optic (EO) coefficients of, not only the polymer thin film, but also the polymer waveguide. Furthermore, the tensor components, both r13 and r33, of the EO coefficient can be measured simultaneously. In contrast with the free space MZ interferometer, the fiber-optic MZ interferometer owns some advantages, such as fewer devices, simple experiment configuration, easy operation, and good stability. The most outstanding advantage is that the second electrode need not be fabricated on the top of the polymer thin film. So, the measurement system is especially
suitable to measure E-O coefficients of the polymer samples on trial. The closed loop control system of the phase bias of the MZ interferometer decreases the requirement of the environment stability and increases the measurement precision.