The application of distributed generation resources and capacitor banks is increasing due to the distribution networks extension and also power demand growth. Determining the installation location and the capacity are two important and effective factors on the network power loss and the network performance improvement. If connected in the right place to the power network, distributed generation power plants and the capacitors have different effects such as loss reduction, voltage profile improvement, and network reliability augmentation. In this paper, in order to reduce the distribution system loss, simultaneous optimal placement of the distributed generation resources and capacitors in radial distribution systems is studied. Crow search algorithm is applied for this purpose. This algorithm works on this idea that the crows chase each other in order to find other crows' food hiding place. The simulation is done on IEEE-33 & IEEE-69 buses network in MATLAB software. The simulation results demonstrate the efficiency of crow search algorithm, comparing to other applied optimization algorithms, in the problem of simultaneous optimal placement of the distributed generation resources and capacitors in radial distribution systems to reduce loss and enhance voltage profile.