The van was on its way from Thakot to Battagram in Khyber-Pakhtunkhwa province when it plunged into the ravine near Kotgala village.
Eighteen passengers on board the van were killed when the driver lost control and the vehicle fell about 150 metres into the ravine, Noor Wali, a police official, said.
He said the rescue teams struggled to retrieve the bodies due to steep slopes and thick foliage.
Road accidents are common in Pakistan where hundreds are killed every year due to traffic accidents.
At least 12 people were killed in a similar incident in Pakistan-occupied Kashmir over the weekend.
Careless driving, bad roads and faulty vehicles are common causes of such accidents.