In this paper we study the equation ϕ 2 i (∇R) = AiR on a mixed 3-structure manifold (M, ξi, ηi, ϕi, g) i∈{1,2,3} , where ∇R is the co-variant derivative of the curvature tensor and Ai's are some 1-forms. We give some examples of such manifolds and show that this equation leads to the important equation ∇R = AiR. That means that the manifold is curvature recurrent. Moreover, we prove that on a mixed 3-Sasakian manifold that equation implies ∇R = 0.