Lom Kao (Thai: หล่มเก่า, pronounced [lòm kàw]) is the northernmost district (amphoe) of Phetchabun province, northern Thailand.

The first record of Mueang Lom is found in Ram Khamhaeng the Great's stone pillar.

In the Rattanakosin era, the area was populated by a large community of Lao people from Vientiane.

Neighboring districts are (from the north clockwise) Dan Sai and Phu Ruea of Loei province and Nam Nao, Lom Sak, and Khao Kho of Phetchabun Province.

Lom Kao district is divided into nine sub-districts (tambons), which are further subdivided into 99 administrative villages (mubans).