Lufthansa is set to pay 65m for a 45% stake in SN Airholding, the owner of Brussels Airlines.
Under the planned deal, the German national carrier would have the option in two years time of acquiring the remaining 55% of the Belgian carrier.
The price for taking full control would be linked to the profitability of Brussels Airlines.
In a statement, Lufthansa said it expected the deal to be completed over the next few weeks.
The statement pointed out that Brussels Airlines which operates flights mainly to Europe but also "specialises in flights to Africa."
Lufthansa has also confirmed that it might be interested in buying a stake in Austrian Airlines.
It has also said it is in talks with Thomas Cook and Tui, two German travel agencies, about merging its low cost carrier Germanwings with the two companies' respective airlines, Condor and Tuifly.
Austrian Airlines is seeking a strategic partner and the Austrian government has put in motion the process to sell its 43% in the national carrier.
Both Lufthansa and Austrian are members of the Star Alliance.
But agency reports have also suggested that Air France and possibly BA might also be interested in a stake in the central European carrier.
* see BTE Analysis