Rio de Janeiro police said officers were fired on during the morning shift change in a favela, or shanty town, called Mangueira.
The fatality was an officer who was shot in the head. Another was wounded in the leg. The assault was blamed on drug traffickers.
So far this year, 88 police officers have been killed in Rio, 10 more than at the same point of last year, the news website G1 said.
The officers were members of a counter-narcotics unit that works close up with people in the very dangerous favelas.
Shootings have been on the rise in recent weeks in this city that just last year hosted the summer Olympic Games.
On average, three people have been killed by stray bullets every day in the first six months of the year.
On Sunday evening, the main road leading to the city's international airport was blocked by gunmen stopping cars and trying to rob people.
Police intervened and a gun battle ensued, triggering panic on a very busy highway that runs through the city's northern suburbs and the downtown area.
Video on social media shows motorists ducking down beside their cars for shelter. Witnesses quoted by Brazilian media said some people jumped into the trunks of their cars.
Others ran away to a nearby police station.
There were no reports of injuries.
The rise in violence has been accentuated by the city's financial woes. Rio is on the verge of bankruptcy and cannot pay its employees on time, including the police.
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