Boso (Italian: Bosone; died after 940?) was a Burgundian nobleman who spent much of his career in Italy, where he became Margrave of Tuscany about 932. He ruled semi-autonomously and was a benefactor of the churches of his region. He lost his office in 936 and probably returned to Burgundy.
Boso was the second son of Count Theobald of Arles and Bertha, illegitimate daughter of King Lothair II. His elder brother Hugh was born in 880/1. His family belonged to the highest ranks of the aristocracy of the Carolingian Empire and were related by marriage to the Carolingian dynasty and the Bosonids, the ruling family of Provence.
After Theobald's death (895), Boso's mother remarried to Adalbert the Rich, then margrave of Tuscany. Boso and Hugh inherited their father's counties. After the Emperor Louis III was blinded by his foes in 905, Hugh assumed the regency in Provence and the county of Arles, while Boso took over the county of Avignon. In 907, Hugh and Boso entered Italy with an army in support of their mother. In 926, after Hugh had become King of Italy, he appointed Boso regent of Provence. In 931 he brought Boso to Italy at the same time as he made his son, Lothair, co-ruler in order to strengthen his position against the powerful margrave Lambert of Tuscany. Lambert was the reputed son of Adalbert and Bertha and half-brother of Hugh and Boso. According to Liutprand of Cremona, the rumours of the time had it that Bertha, unable to conceive, in order to safeguard her second husband's succession, had feigned pregnancy and presented as her own two sons, Lambert and Guy, who were actually the children of others.