The 78-year-old woman was crossing Mauchline Road, Mossblown, Ayrshire at around 9.25am on Friday when she was hit by a grey Volkswagen Golf heading east.
She was taken to Ayr Hospital where her condition is described as critical.
The 84-year-old driver of the car was uninjured.
The road was closed for several hours as crash scene investigators made inquiries.
Officers are appealing for anyone with any information to contact them on 101.