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, Prachin Buri province. It passes Amphoe Si Maha Phot, Mueang Prachinburi and Ban Sang.
The river merges to the Nakhon Nayok River to be the Bang Pakong River at the border of Amphoe Ban Sang and Amphoe Bang Nam Priao, Chachoengsao province.