Finite trigonometric sums appear in various branches of Physics, Mathematics and their applications. For p, q to coprime positive integers and r ∈ Z we consider the finite trigonometric sums involving the product of three trigonometric functionsIn this work we establish a reciprocity law satisfied by S (p, q, r) in some particular cases. And we compute explicitly the value of the sum S (p, 1, 0) = p−1 k=1 csc 2 πk p .