In a ceremony marked by pomp and tight security, the new president of Latin America's biggest economy pledged to uphold the constitution as he began his four-year mandate.
The longtime politician and former paratrooper intends to open up the country's protectionist economy to the free market, and prioritise business interests ahead of environmental concerns. He has also vowed to cut bureaucracy and halt corruption.
Bolsonaro's praise for aspects of Brazil's 1964-1985 military dictatorship stirred concerns among some voters but his supporters have high hopes for the new presidency.
The new leader has been compared to Donald Trump and shares the same straight-talking, provocative style.
US Secretary of State Mike Pompeo was invited to the ceremony but the leaders of several leftist Latin American countries were excluded from the guest list.
Bolsonaro has promised a more forceful foreign policy, declaring he will do all he can to challenge leftist-ruled Venezuela and Cuba.
Bolsonaro's predecessor Michel Temer finished his term as Brazil's most unpopular leader ever.