In this paper, the second-order mean and double-frequency wave loads on the ISSC TLP in regular waves are investigated. The second-order wave loads on the compliant (massless-spring-supported) TLP are compared with those on the stationary TLP in order to see the effect of body motions. A higher-order boundary element method (HOBEM) with free-surface Green function is used for the computation of the first- and second-order hydrodynamic loading. In particular, the capability of HOBEM in calculating the second spatial derivatives of the first-order potential on the body surface is demonstrated. The numerical results for the stationary ISSC TLP are compared with Matsui et al's (1992) experimental results, and reasonably good agreement is observed.