The Prachin Buri River (Thai: แม่น้ำปราจีนบุรี, rtgs: Maenam Prachin Buri, Thai pronunciation: [mɛ̂ːnáːm praː.tɕiːn buriː]) begins at the confluence of the Phra Prong, Hanuman, and Prachantakham rivers in amphoe Kabin Buri, Prachinburi Province. It passes amphoe Si Maha Phot, Mueang Prachinburi, and Ban Sang.
The river merges with the Nakhon Nayok River to become the Bang Pakong River at the border of amphoe Ban Sang and amphoe Bang Nam Priao, Chachoengsao Province.