This study has been carried out to investigate the properties of green sand as system sand containing various organic core sand, such as Shell core, Cold Box core and Pep Set core sand. The permeability of the system sand containing Pep Set core sand was decreased, but increased from containing 5wt.% core sand. The compressive strength and the surface stability index were increased up to containing 5wt.% core sand, but decreased with containing more than 5wt.% core sand. The compactability index was increased with the ratio of core sands. In case of the system sand containing Cold Box core sand, the permeability and the compressive strength were increased with the ratio of core sands, and the surface stability index and the compactability index was a little increased with the ratio of core sands. In case of the system sand containing Shell core sand, the permeability and the compressive strength were a little decreased with the ratio of core sands, and the surface stability index and the compactability index was a little increased with the ratio of core sands. The bonded force of the system sand mixed with core sands were poor and the grain surface was rough. The loss of ignition of system sand containing shell core sand were more than it with others, it has been found that the system sands containing organic core sands have to reclaim for using molding sand. (Received December 31, 1997)