The Resource Constrained Project Scheduling problem (RCPSP) has been considered as a scheduling problem which has a wide range of applications in construction industries, manufacturing, production planning and project management domains. To solve such RCPSPs, in this paper we propose a hybrid algorithm that utilizes the strengths of both differential evolution (DE) and cuckoo search (CS) algorithm in one framework called hybrid differential evolution with cuckoo search (DECS) algorithm. In it, a selection mechanism based on the solutions' quality and populations' diversity is used to select the most appropriate algorithm during the evolutionary process. A linear population reduction mechanism is utilized to update the DE population size. A number of data sets of single-mode RCPSPs from the project scheduling library (PSPLIB) have been considered and solved by the proposed hybrid DECS algorithm. Computational results and comparisons with some recent state-of-the-art algorithms show that DECS is able to produce very high quality results.