Phatthalung is located on the Malay Peninsula. To the east it borders the large shallow Songkhla lake, while the west is covered by mountains of the Nakhon Si Thammarat chain. The Khao Pu - Khao Ya National Park is located in these mountains at the border to Trang. Phatthalung was formerly known as Mardelong in Malay, especially during the time when the region came under Malay-Muslim influence.