The 61-year-old millionaire is Mozambique's third president since independence from Portugal in 1975 after Chissano and founding president and liberation hero Samora Machel, who died in suspicious circumstances in a plane crash in 1986.
Guebuza was sworn in by Rui Baltazar Dos Santos Alves, who heads Mozambique's Constitutional Council, and pledged to "dedicate all my energies to the defence, promotion and consolidation of national unity, human rights, democracy and welfare of the Mozambican people".
Guebuza won the December 1-2 poll with about 64 percent of the vote against 32 percent for the candidate of the former Mozambique National Resistance (RENAMO), which laid down its guns in 1992 after a long and brutal civil war.
Guebuza has pledged to continue economic reforms started by Chissano, which have won Mozambique plaudits from the World Bank and International Monetary Fund and pushed economic growth to an average annual 10 percent over the past decade, one of the highest in the world.