The Foreign Ministry said Steinmeier had travelled to the northern city of Herat for the official handover of a water treatment facility built with German help and to take a firsthand look at other developments in the region.
Germany is supporting restoration of Herat's historic old centre and has strong ties to the city's university.
There are currently 3,500 German soldiers stationed in the northern part of Afghanistan as part of NATO's ISAF mission in the country. The German government recently approved raising the military's mandate by another 1,000 troops, but the move must still be approved by parliament.
Berlin has also committed €1.1 billion for reconstruction projects in the country through 2010.