The two West African countries are run by military juntas that seized power in coups.
The military leaders of Mali and Niger said Tuesday that they would both scrap tax agreement with France, continuing an unravelling of ties with Paris while tightening their own relations.
In a joint statement, the neighbouring West African nations cited "France's persistent hostile attitude towards our states" and "the unbalanced nature of these agreements, which result in a considerable loss of revenue for Mali and Niger".
The tax accords with former colonial ruler France will end "within three months", the military leaders of each country said.
The practical repercussions of the decision were not immediately clear.
The French tax authorities' website states that France has had agreements with Mali, since 1972, and Niger, since 1965, "aimed at avoiding ('eliminating' in the case of Niger) double taxation and establishing rules for mutual assistance" in fiscal matters.
The agreements cover personal and corporate income tax, inheritance tax and registration duties.
The decision by Mali and Niger is the latest act of defiance towards France since military forces seized power in Bamako in 2020 and in Niamey earlier this year.
Burkina Faso, another Sahel country whose military took over last year, had already denounced its tax treaty with France earlier this year.
The three African countries, which face similar problems including militia militants, formed an alliance this year and their foreign ministers have recently proposed the creation of a confederation.