In this paper the Archimedean property and the nilpotency of t-norms on the lattice LI is investigated, where LI is the underlying lattice of interval-valued fuzzy set theory (Sambuc, 1975) and intuitionistic fuzzy set theory (Atanassov, 1983). We give some characterizations of continuous t-norms on LI which satisfy the residuation principle, T (D, D) ⊆ D, the Archimedean property and nilpo