This paper presents a Passivity Based Control (PBC) for a dc microgrid. PBC is commonly used in electrical systems such as power electronics converters and electric machines, but there are few applications in microgrids operating in island mode. PBC is based on properties of passive systems and energy exchange between subsystems. The proposed strategy performs primary and secondary control of the hierarchical architecture. Local communications and measurements are needed at the nodes where dc/dc converters are placed. Simulation studies are performed in MATLAB to validate the control in a realistic test system composed of renewable energies sources, loads and energy storage units. Results show that the proposed control ensures stability and fast response of the dc-bus voltage under different operating conditions.