Radelchis I (also Radalgis) (died 851) was the treasurer, then prince of Benevento from 839, when he assumed the throne upon the assassination (possibly his instigation) of Sicard and imprisonment of Sicard's brother, Siconulf, to his death, though in his time the principality was divided.
Radelchis I (juga Radalgis) (wafat 851) merupakan seorang bendahara, kemudian Pangeran Benevento dari tahun 839, ketika ia naik tahta setelah pembunuhan (kemungkinan atas rencananya) Sicard dan memenjarakan saudara Sicard, Siconulf, sampai kematiannya, meskipun pada masanya kerajaan itu dibagi.