Lew was on a one-day visit to Greece after attending a Group of 20 summit in Russia.
In an hour-long meeting with Finance Minister Yannis Stournaras, Lew discussed Greece's austerity program, its long-term prospects, and visits the so-called troika of Greece's creditors the European Commission, the European Central Bank and the International Monetary Fund have made to Greece, said Dimitris Kanellisa, a Finance Ministry spokesman.
Later, Lew met with Prime Minister Antonis Samaras at an unusual setting, the Acropolis Museum, not the Greek leader's office.
Samaras is due to meet President Barack Obama in Washington next month.
"Our talks focused on the obvious challenges of stability and growth," Samaras told reporters before he and Lew dined under the Acropolis. "We need stability in the region to boost growth, which for us means jobs, investment opportunities and prosperity."
Lew said the U.S. is closely following Greece's efforts to end its economic crisis.
"We recognize the difficult decisions and sheer sacrifices made by Greece in the past few years, as well as the challenges that remain," he said. "Continued reform will be essential to laying the foundations for future growth."
Lew also said, "Engagement with Europe remains at the top of my agenda because U.S. jobs and growth are inextricably linked with European prosperity."