The woman was driving her Honda Accord south on Atkins Avenue in East New York when her vehicle was hit by the truck, which was headed easton Cozine Avenue about 1:50 a.m., officials said.
The woman died at the scene. Her name hasn't been released.
The postal truck driver, 48, had a head injury. He was taken to Brookdale University Hospital in stable condition.
The cause of the crash remains under investigation, but police say the woman who died may have run a stop sign.