(927–c. 1090), Iranian dynasty that ruled in the Caspian provinces of Gurgān and Māzandarān. The founder of the dynasty was Mardāvīz ebn Zeyār (reigned 927–935), who took advantage of a rebellion in the Sāmānid army of Iran to seize power in northern Iran. He soon expanded his domains and captured the cities of Hamadān and Eṣfahān. Mardāvīz was murdered in 935, and Zeyārid power thereupon disintegrated.

During subsequent hostilities between the Sāmānid and the Būyid dynasties, the Zeyārids changed their allegiance several times and thus were able to maintain their autonomy. But with the consolidation of Ghaznavid power, the Zeyārids acknowledged that dynasty's suzerainty and entered into various marriage alliances with it. When the Seljuqs occupied Māzandarān in the mid-11th century, the Zeyārids were forced to withdraw into the mountainous territory on the southern Caspian shores, where they ruled until about 1090.

The Zeyārids were distinguished patrons of the arts. The noted Islāmic geographer and scientist al-Bīrūnī (Bīrūnī, al-) resided for many years at the court of Qābūs I ebn Voshmagīr (reigned 978–1012). Keykāvūs (reigned 1049–90) himself was the author of a famous manual for princely behaviour, the Qābūs-nāmeh (“Mirror for Princes”).