Abstract. We investigate sharp estimates of integral functionals for operators on the set T n of real trigonometric polynomials f n of degree n ≥ 1 by the uniform norm f n C2π of the polynomials and similar questions for algebraic polynomials on the unit circle of the complex plane. P. Erdös, A.P. Calderon, G. Klein, L.V. Taikov, and others investigated such inequalities. In this paper, we, in particular, show that, for 0 ≤ q < ∞, the sharp inequality D α f n Lq ≤ n α cos t Lq f n ∞ holds on the set T n for the Weyl fractional derivatives D α f n of order α ≥ 1. For q = ∞ (α ≥ 1), this fact was proved by P.I. Lizorkin (1965). For 1 ≤ q < ∞ and positive integer α, the inequality was proved by Taikov (1965); however, in this case, the inequality follows from results of an earlier paper by Calderon and Klein (1951).