Klaus Berntsen (12 June 1844 – 27 March 1927) was a Danish politician, representing the Liberal party, Venstre.

After the beginning reunion of the old Venstre groups he played a greater role as a minister that led to the forming of his own cabinet.

He was a personal friend of King Frederik VIII and enjoyed the king's support but his government was accused of lacking social understanding.

1913 he proposed the revision of the Constitution that was carried through by the second Zahle Cabinet.

When he retired from politics in 1926 he was one of the oldest Danish active parliamentarian politicians ever.