Tahmasp I (Persian: طهماسب; March 3, 1513- May 14, 1576) was the Shah (emperor) of the Safavid Empire in Persia. He reigned from 1524 to 1576.

Tahmasp I was the son of the first Shah Ismail I of the Safavid Empire. He inherited the throne at the age of 10 and was controlled by the leaders of the Chizbash tribe in his childhood. He constantly fought against the Chizbash people as an adult, suppressing all their attempts and strengthening the centralization of power in Persia.
In 1528, Tahmasp I defeated the Uzbeks in the Battle of Gam, and the king of the Bukhara Khanate, S ü yunchi, was wounded and died several years later.
Tahmasp I annexed the Shirvan Khanate in 1538 and incorporated Sheki into Persia in 1551. In 1544, he helped the Mughal Emperor Humayun of India restore the throne. Tahmasp I therefore received Kandahar as a reward. Around 1548, Tahmasp I moved the capital of the dynasty from Tabriz to Gazvin.
During the reign of Tahmasp I, Persia continuously fought against the Ottoman Empire and the Uzbek Khanate (later renamed the Bukhara Khanate). In the early Ottoman Safavid War (1532-1555), the Ottoman Empire eventually acquired the contemporary equivalent of Iraq, and Tahmasp had to form the Habsburg Persian Alliance with the Habsburgs of Austria in the 1530s to jointly confront the Ottoman Empire militarily. In 1553, Tahmasp I resisted the attack of Ottoman Sultan Suleiman I. In 1555, Tahmasp I signed a peace treaty with the Ottoman Empire.

In 1565, Tahmasp I abolished tariffs. He died in Gazvin in 1576.