Zahhak Castle (or citadel) is a castle in East Azerbaijan Province, Iran. It is named after Zahhak, a figure in Persian mythology. According to various experts, it was inhabited from the second millennia BC until the Timurid era. It was first excavated in the 1800s by British archeologists. Iran's Cultural Heritage Organization has been studying the structure in 6 phases.

The castle was first discovered by a British army officer in 1830. He noticed that the ruins were quite ancient, dating back at least two thousand years. In recent years, Zahhak Castle has been unearthed slowly by archaeologists who have discovered that different parts of the castle were built in later periods. During this time, Zoroastrianism was the religion of the ruling kings, who likely used part of the castle for a fire temple.