Prepare rice according to package directions; set aside.
Brown sausage in a Dutch oven, stirring to crumble. Add onion and celery; sauté until vegetables are tender. Drain off pan drippings.
Stir in reserved rice, oysters, and 1 cup parsley. Pour mixture into a 13- x 9- x 2-inch baking dish. Bake at 350° for 25 minutes. Remove from oven; sprinkle remaining 1 cup parsley over mixture, and bake an additional 5 minutes. Serve hot.