Guglionesi (Italian: [ɡuʎʎoˈneːzi, -eːsi]; local dialect: Ujuniše [ujəˈniːʒə] or Uiniše [wi.əˈniːʒə]) is a town and comune in Molise, southern Italy, about 50 kilometres (31 mi) from Campobasso.

Founded in the 5th century BC, at the time it was known as Uscosium or Usconium and together with Pescara, Ortona, Lanciano, Vasto and Larino, it was one of the most important centers of the Frentani, an Italic people that was part of the Samnites confederations.

In 1315 King Robert of Anjou gave Collenisio to his brother Peter, Count of Gravina, and at his death, his daughter Agnese inherited the city.

In 1496, after the death of René of Anjou, his cousin Charles VIII of France descended to Italy with a large army and conquered Naples.

The French entered Guillonisi (only by the betrayal of the guards of the Frentan door) and plundered the entire village, demolished the two castles and the towers and killed or raped most of the people.