Elastic optical networking is a promising technology for the next generation of optical core networks and the routing, modulation and spectrum assignment (RMSA) problem is one of its key issues. The RMSA problems for immediately reservation (IR) and advance reservation (AR) requests have been widely researched. Malleable reservation (MR) requests are another kind of important traffics in elastic optical networks (EONs). However, the RMSA problem for MR requests has not been well considered. In this paper, we investigate the RMSA problem for MR requests in EONs and propose an algorithm named Min-RRD. The algorithm assigns frequency-time blocks with the minimum sum of three indexes, namely number of used resources (Rused), number of impacted resources (Rimpacted) and distance to corner (Dcorner), to MR requests. Simulation results show that the proposed algorithm has a lower blocking probability and a smaller delay than the existing algorithm. Hence, it is a well-performed RMSA algorithm.