We investigated the formation of single-crystal CH3NH3PbCl3 and CH3NH3PbI3 perovskites by cast-capping method. This very simple but high efficiency technique based on modified solution process was successful to grow large-domain single crystals up to a millimeter size. Their X-ray diffraction patterns revealed that both crystals grew in the cubic form. The (100) planes of both crystals grew predominantly in contact with the substrate surface. The present technique helps further studies as an alternative method to fabricate high performance functional devices.