Mazara del Vallo (Italian pronunciation: [madˈdzaːra del ˈvallo]; Sicilian: Mazzara) is a town and comune in southwestern Sicily, Italy, which lies mainly on the left bank at the mouth of the Mazaro river, administratively part of the province of Trapani.

It is an agricultural and fishing centre and its port gives shelter to the largest fishing fleet in Italy.

Mazara was founded by the Phoenicians in the 9th century BC, with the name of Mazar (the Rock). It then passed under the control of Greeks, Carthaginians, Romans, Vandals, Ostrogoths, Byzantines, before being occupied by the Arabs in the year 827 AD. During the Arab period, Sicily was divided into three different administrative regions, Val di Noto, Val Demone and Val di Mazara, making the city an important commercial harbour and centre of learning. The city centre, known as the Kasbah, retains Arab architectural influences.

In 1072, Mazara was conquered by Normans, headed by Roger I. During that period, in 1093, the Roman Catholic Diocese of Mazara del Vallo was instituted.