Alstonia macrophylla is a tree with a straight trunk and a high, narrow crown. It can become up to 30 meters tall. The trunk and branches contain a white latex. The bark is smooth and has a light grey color. Leaves are in whorls of three to four, simple, penni-veined, membranous, and glabrous above. Leaf-blades are 10 to 50 centimeters long, 5 to 15 cm wide, widest in or above the middle, and cuneate at the base. Flowers are about 7 mm in diameter, white, with narrow corolla tube, placed terminal on twigs. Fruits are about 30 centimeters long, green and filled with many small hairy seeds that are dispersed far and wide by the wind. The heartwood is yellowish, with a straight and shallowly interlocked grain with a moderately fine to rather coarse texture