Police were alerted after the four disappeared in Lam Klong Ngu stream near a reservoir at Srinakarin Dam at about 10.30am.
Witnesses said none in the group wore life jackets. It was believed the women were tipped from their raft and drowned in an area known to have strong currents and whirlpools.
Divers searched for their bodies for hours and managed to retrieve all of them late in the evening.
They were identified as Nattamon Lekbamrung, 39, Narumon Kamolpattana, 33, Yuwadee Kongpichiansri, 29, and Papassorn Lohanantachai, 37. All were employees of Science For Kids, a Bangkok-based company which provides science edutainment for young school children.
The protected area is named after a stream that snakes through limestone mountains and a series of caverns along its course, which are highlights for park visitors.
Park official Jaripat Samretkij said rafting trips along the Lam Klong Ngu stream are allowed between March and April, but must receive permission first, and be guided by officials only. He said the park was checking to see if the women were customers of a private tour rafting operator and entered the closed park area.