The device was detonated remotely when a police vehicle on a routine patrol passed along a road on the outskirts of Quetta, the capital of Baluchistan province, which suffers from Taliban, sectarian and separatist violence.
It was the second fatal attack on police in the city in two days.
"The bomb blast wounded four policemen and one of them died in hospital,"Â senior police official Sikandar Tareen told AFP.
"It is not immediately clear who targeted the police," he said. Another police official confirmed the attack and casualties. There was no immediate claim of responsibility.
Police are frequently attacked in Baluchistan. On Tuesday, senior police official Shah Nawaz Khan was assassinated in Quetta in a drive-by shooting claimed by Al-Qaeda-linked militant group Lashkar-e-Jhangvi (LJ).
On April 29, British aid worker Khalil Dale was found beheaded in Quetta, nearly four months after he was kidnapped in the city.
There has been no claim of responsibility for his murder.
