The mill, located around 120km from Sofia, makes brown kraft paper.
The fire damaged its single paper machine, which had capacity of 100,000tpa.
In a statement, Mondi said: “After evaluating the options for repairing the mill and the ongoing investment required for the mill to remain competitive into the future, Mondi has concluded that closing the mill and serving customers out of its network of other kraft paper mills is the best course of action overall.”
The decision will affect around 300 Mondi Stambolijski employees.
Mondi said the net closure costs were estimated at €100m “primarily related to a non-cash asset impairment which we will book as a special item”.
Last year Mondi invested in reducing water use by the site’s pulp and paper processes by installing a turbo blower on the paper machine, and a cooling tower in the turbine and evaporation area.