Motivated by the recent work of Wu and Yau on the ampleness of canonical line bundle for compact Kähler manifolds with negative holomorphic sectional curvature, we introduce a new curvature notion called real bisectional curvature for Hermitian manifolds. When the metric is Kähler, this is just the holomorphic sectional curvature H, and when the metric is non-Kähler, it is slightly stronger than H. We classify compact Hermitian manifolds with constant non-zero real bisectional curvature, and also slightly extend Wu-Yau's theorem to the Hermitian case. The underlying reason for the extension is that the Schwarz lemma of Wu-Yau works the same when the target metric is only Hermitian but has nonpositive real bisectional curvature.It is a natural question to ask when will a Hermitian manifold have constant real bisectional curvature. To this end, we have the following:Theorem 1.4. Let (M n , g) be a compact Hermitian manifold whose real bisectional curvature is constantly equal to c. Then c ≤ 0. Moreover, when c = 0, then (M, g) is a balanced manifold with vanishing first, second, and third Ricci tensors, and its Chern curvature satisfies the property R xyuv = −R uvxy for any type (1, 0) complex tangent vectors x, y, u, v.We would like to propose the following conjecture:Conjecture 1.5. Let M n (n ≥ 3) be a compact Hermitian manifold with vanishing real bisectional curvature c. Then c = 0, and its Chern curvature tensor R = 0.By Boothby's theorem, compact Hermitian manifolds with vanishing Chern curvature are precisely the compact quotients of complex Lie groups equipped with left invariant metrics.Besides the constant real bisectional curvature cases, more generally, it would certainly be very interesting to try to understand the class of all compact Hermitian