The Ricci dark energy ( RDE ) proposed to explain the accelerating expansion of the universe requires its parameter \alpha < 1 , whose value will determine the behavior of RDE .
In this Letter , we study the scalar perturbation of RDE with and without matter in the universe , and we find that in both cases , the perturbation is stable if \alpha > 1 / 3 , which gives a lower bound for \alpha theoretically .