The former Portugal international has completed his move back to the Spanish top flight after he had opted to leave Besiktas
The former Portugal attacker recently terminated his contract with Besiktas, and has now inked a two-year deal with the Catalan outfit.
Simao, 32, came through the ranks of the Sporting Lisbon youth academy, and also wore the jerseys of Barcelona, Benfica and Atletico Madrid before joining Besiktas in January 2011.
He won the Turkish Cup in his first season at the Istanbul giants, but has now returned to the Catalan capital again after 18-months in Turkey.
Espanyol previously secured the services of Sergio Tejera, Wakaso, Joan Capdevila and Diego Colotto.