Morales did not provide more details on the referendum or the questions voters would be asked.
Allies of the president hold a majority in the lower house of congress, but not in Bolivia’s senate.
Bolivia’s constitutional changes are at the centre of a power struggle between him and his opponents, concentrated in lowland areas, that are also home to large natural gas fields.
Those opposed to Morales’ attempted reforms, shut down large parts of the country last week in a strike after a draft of the constitution was passed in an elected constitutional assembly boycotted by the opposition.
That vote triggered violent protests in the southern city of Sucre, the seat of the assembly, killing at least three people.
As Morales made his announcement, four provincial governors were visiting the Organisation of American States (OAS) in Washington to criticise the actions of the Morales administration.
David Choquehuanca, Bolivia’s foreign minister, rejected mediation by the OAS, and Morales said the conflict should be settled at home.
He said: ‘It’s not about complaining outside the country, but about submitting ourselves to the will of the people.”