The fatigue is one of the most important considerations in the design of tesion-leg platform (TLP) tendons. Due to the natural frequencies of the vertical-plane motions of the platform that are substantially higher than the frequency band of the ocean waves and the relatively low damping, the resonant high-frequency oscillations caused by higher-order nonlinear wave excitations may have a significant effect on the fatigue damage. In this paper, the fatigue damage of the TLP tendons is predicted with consideration of the second-order sum-frequency wave load effects. A spectral method of analysis based on the Palmgren-Miner rule and the S-N curves is adopted to evaluate the cumulative damage of the tendons during the service life of the platform. Assuming the stress response spectra to be narrow-banded, the stress amplitudes are considered to obey the Rayleigh probability distribution. Through an example study for the single-column TLP, it is revealed that the second-order sum-frequency wave loads contribute to a dominant part of fatigue damage of the TLP tendons.