The matter was decided at a cabinet meeting in Brussels on Thursday morning.
The two reactors are already 40 years old.
The Belgian Government says it's necessary to keep the reactors running for longer in order to ensure energy supplies. Uncertainty about whether or not reactors Doel 3 and Tihange 2 can be relied on as energy suppliers, the planned closure of other power plants and difficulty in importing energy all played a role in the decision.
Belgium will have to invest in the plants to ensure they remain safe. Talks with generator Electrabel are planned.
Opposition party Groen has already voiced its disappointment. The ecologist's' floor leader Kristof Calvo took to Twitter to exclaim "The government's ditching the nuclear exit."
Belgium's ecologists say that keeping the nuclear power plants open for longer isn't safe and will not lead to energy security: "Belgium will remain reliant on antiquated and unreliable nuclear energy."
Groen and Ecolo estimate the decision will cost the taxpayer up to 700 million euros: "These are investments that could have gone to renewables, energy conservation and flexible gas-powered plants. These are companies that could have created jobs. This is now being prevented. The extension is a Christmas present to France's GDF Suez and generator Electrabel."