Disclosed is a refrigerator rail assembly for guiding a storage box while the storage box is being extracted from or retracted into a space of a refrigerator. The refrigerator rail assembly includes: a guide rail provided on a side of the storage space to extend in the front-to-rear direction of the storage space, the guide rail having a guide channel formed in the longitudinal direction of the guide rail and opened at a side thereof; a movable rail having a guide channel formed in the longitudinal direction of the movable rail and opened at a side opposed to the guide channel of the guide rail, the storage box being removably installed to the movable rail; an intermediate rail having a pair of guide flanges which are inserted into the guide channels, respectively; and a plurality of ball bearings interposed between the guide channels and the guide flanges. The guide rail and the movable rail move in relation to the intermediate rail, so that the storage box is extracted from or retracted into the storage space.