Lam Sonthi (, ) is a tributary of the Pa Sak River. It originates at the Ruak and Phanghoei mountains in the border area of Lam Sonthi district, Lopburi province and Si Thep, Phetchabun province.
The Lam Sonthi river, a tributary of the Pa Sak River, originates in the mountainous region bordering Lam Sonthi district in Lopburi province and Si Thep in Phetchabun province.