Dong Phaya Yen or Dong Phya Yen[2] (Thai: ทิวเขาดงพระยาเย็น [doŋ pʰajaː jen], lit. Jungle of the Cold Lord) is a mountain range in Phetchabun, Chaiyaphum, Lopburi, Saraburi and Nakhon Ratchasima Provinces, Thailand.
Since the Dong Phaya Yen is less compact and lower in height than the mountain ranges to the north and to the south, the first roads and railroads communicating the vast region of Isan with the capital Bangkok were built across these mountains. Before the construction of the railroad in the beginning of the 20th century, communication between these two parts of Thailand was difficult. The survey for building of the Northeastern Line of the State Railway of Thailand began in 1887.