a b s t r a c tLet F q be a finite field with q elements, l an odd prime, and t, v positive integers such that l v |(q − 1) and gcd(t, l) = 1. In this paper, we give a combinatorial result and use it to determine the weight distribution of a cyclic code of length tl m with t|(q − 1), which is an open question in . Moreover we compute the weight distributions of cyclic codes of length tl m , where q ≡ 3 (mod 4) and t = 4 or 8.