"You enter office at a difficult time for your country as well as for the eurozone as a whole, in which great hopes and expectations are directed at you," Merkel wrote to Monti in a letter congratulating him on his appointment.
"You and your government are called upon to quickly decide and implement crucial and necessary reform measures," she wrote.
The German leader also said that she was pleased to work with Monti "on overcoming the common challenges in the eurozone and for the good of Europe," in the letter released by her office.
And she expressed the hope that "our cooperation will further consolidate and deepen the traditionally good and deep friendship between our peoples."
Monti, who was formally sworn in Wednesday, is set to unveil his economic programme Thursday, under heavy scrutiny from global leaders, financial markets and parliamentarians wary of hard-hitting reforms.
The 68-year-old - a widely respected economics professor and former European Union commissioner - replaces Silvio Berlusconi, who was forced to resign after a parliamentary revolt and a wave of market panic.