Red mulberry is a medium-sized tree with a short trunk and a broad, rounded crown.
Leaves are alternate, simple, 4–8 inches long, usually lacking lobes but some leaves with 1–3 lobes; teeth dense; tip pointed. Three main veins arise from the base. Undersurface hairy, paler than above. Bleeds milky sap. Leaf stalk hairy.
Bark is thin, dark brown to gray with an orange tint, grooves shallow, ridges narrow, tight, sometimes with loose scales.
Twigs are reddish-brown to light greenish-brown, smooth, slender, bleeding milky sap.
Flowers April–May; male and female flowers on the same tree or on different trees. Male catkins 2–3 inches long; female catkins 3/8 inch long.
Fruits June–August, blackberry-like; red at first, ripening to purplish-black, cylindrical; ¾–1¼ inches long.
Similar species: The introduced white mulberry (M. alba) has leaves smooth underneath, more often lobed, with smooth leaf stalk; its fruits are rounded or oval and start out white or pink; its catkins and leaves are smaller.