Belsize Park was recorded as Balassis in 1317 from the Old French wording bel asis, which means 'beautifully situated', and was no doubt aptly named from the manor house and park which were once on the present site of Belsize Square. No fewer than ten streets in this part of North West London include Belsize in their name.

Before the station opened plain BELSIZE was considered for the name, but it was opened as BELSIZE PARK on 22 June 1907.