The incident took place around 5 p.m., Thursday, Dec. 17, on Jerusalem Avenue in Levittown, said the Nassau County Police.
According to detectives, the man, 46, was walking southbound on Jerusalem Avenue in the vicinity of Mallard Road was struck by a United States Postal vehicle traveling southbound on Jerusalem Avenue.
As a result of the collision, the pedestrian suffered multiple trauma injuries to his head and body.
He was transported to an area hospital and is in serious condition.
The 62-year-old driver remained at the scene, police said.
An investigation is ongoing.
Click here to follow Daily Voice Brentwood and receive free news updates.