Their blockade cut the main route between the South and other regions of Thailand for more than an hour.
The protesters, who came from various provinces such as Kanchanaburi, Uthai Thani and Rayong, also tried to block alternative routes.
The farmers dispersed only after Prachuap Khiri Khan Governor Veera Sriwattanatrakoon informed them that the National Pineapple Development Policy Committee had approved an Bt800million budget to ease their plight.
Veera said the money would be used to buy 200,000 tonnes of pineapple at Bt4 per kilogram.