The Battle of Chickasaw Bayou, also called the Battle of Walnut Hills, fought December 26–29, 1862, was the opening engagement of the Vicksburg Campaign during the American Civil War. Confederate forces under Lt. Gen. John C. Pemberton repulsed an advance by Union Maj. Gen. William T. Sherman that was intended to lead to the capture of Vicksburg, Mississippi.

On December 26, three Union divisions under Sherman disembarked at Johnson's Plantation on the Yazoo River to approach the Vicksburg defenses from the northeast while a fourth landed farther upstream on December 27. On December 27, the Union army pushed their lines forward through the swamps toward the Walnut Hills, which were strongly defended. On December 28, several futile attempts were made to get around these defenses. On December 29, Sherman ordered a frontal assault, which was repulsed with heavy casualties, and then withdrew. This Confederate victory frustrated Maj. Gen. Ulysses S. Grant's attempts to take Vicksburg by a direct approach.