Alexander III (870 - 913) was son of Basil I and brother of Byzantine emperor Leo VI.

Alexander had been named co-emperor during Leo's rule. Upon Leo's death in 912 Alexander became full emperor, and regent for Leo's son Constantine. His reign was very brief, and while the Bulgars were preparing for war against the Empire in 913, Alexander died. On his deathbed he named Constantine his heir (the boy became Constantine VII).