Preheat oven to 400°.
Peel sweet potatoes, and cut lengthwise into 1/4-inch-thick slices. Arrange potato slices in a single layer in a 13- x 9-inch baking dish.
Combine orange juice, margarine, and cinnamon in a small bowl, stirring well. Pour over sweet potato slices. Bake, uncovered, at 400° for 30 minutes or until tender, turning once.
Tip: Sweet potatoes are rich in beta carotene, vitamin C, and vitamin E--nutrients that can help prevent heart disease and certain cancers.