Bandar-e Mahshahr (Persian: بندرماهشهر‎, also Romanized as Bandar-e Māhshahr, Bandar-e Ma‘shūr, Bandar Mah-Shahr, Bandar Mah Sharh, Bandar-mashoor, Bandar-Mashour, Bandar Ma‘shūr, Bandar Mashur; also known as Bār Andāz, Māhshahr, Mah Shahr, and Mashur) is a city in and the capital of Mahshahr County, Khuzestan Province, Iran. At the 2006 census, its population was 109,927, in 24,110 families.

Bandar-e Mahshahr is an ancient city and port in the Khuzestan province in southwestern Iran. Originally known as Reyshahr and then Machuleh, it eventually came to be known as Bandar-e Ma'shoor. The name changed again in 1965, this time to Bandar-e Mah Shahr.

The word Mah-shahr is Persian and means "city of the moon". The city's port is one of the most important in Iran, exporting gas and refinery products from Abadan.

Mahshahr has two universities. Islamic Azad University of Mahshahr and Amirkabir University of Technology, Mahshahr campus. Both universities concentrate on engineering programs, especially petroleum and petrochemical engineering. Most of its people are Persian-speaking. Local Persians are mostly of Qanavati and Bandari families. There is also a local Arab-speaking minority whose roots go back to Qabban in Iraq.