Mechanical bending characterizations are performed on flexible radio-frequency (rf) single-crystalline germanium (Ge) diodes on plastic substrates. Transversal and longitudinal, convex, and concave bendings are conducted. Dc and rf experimental results indicate different performance dependence of the diodes on different types of bending strains, at different biases. Equivalent circuit model is employed to analyze the underlying mechanisms that affect the characteristics of the flexible Ge diodes under bending conditions. Less performance variations are observed for the flexible Ge diodes than the Si diodes with bending strains. The flexible single-crystalline Ge diodes demonstrate good high frequency response and robustness for mechanical bendings.