The trustees of Wykeham House School in Fareham had warned last month its future was in doubt.
A statement blamed falling numbers and said most children had found alternative schools.
The school offered single sex teaching for both boys and girls, charging fees of up to Â£4,100 per term. Both the boys' and girls' sites are to close.
Wykeham House School was established, initially as a girls' school, in 1913 and has about 120 pupils.
A new boys' senior school site opened in September 2014.
Its website said the school prided itself on its "small classes and nurturing environment".
Chair of trustees John Charles, said: 'We are sorry to be closing the doors on such a wonderful school.
"We have worked hard to explore different options to secure a future for our school but in the face of reducing pupil numbers and a shrinking market place for single sex education we have had to take the sad decision to close the school.'
The school statement said it would close at the end of the autumn term.
An independent school in Hampshire has confirmed it will close because of "financial pressure".