Herman Deinum is a Dutch bass guitarist. He is best known as a member of Sweet d'Buster.

Deinum learned to play the piano at the age of ten and subsequently played guitar in The Rocking Specials, a band from Kampen, organ with Gigs, and lead guitar with The Mozarts. In 1967, he succeeded Jaap van Eik as bass guitarist in the Zwolle band Blues Dimension, where he formed a rhythm section with a childhood friend, drummer Hans la Faille.

The duo moved on to Cuby and the Blizzards in 1969, played in the group Cyril around Cyril Havermans in 1974, and formed the rhythm section of Sweet d'Buster from 1976 onwards. After the group's breakup, Deinum played with the Harry Muskee Gang from 1982 to 1984. A long hiatus followed. In 1991 he founded the Herman Deinum Bluesband and since 1996 he played with La Faille again with Cuby and the Blizzards. After a conflict in 2010 surrounding PR man Henk Aa, Deinum left the band. Since 2019 Deinum has played in Still Believe.