As an enzyme with a critical role in de novo purine synthesis, adenylosuccinate lyase (ADSL) expression is upregulated in various malignancies. However, whether ADSL possesses noncanonical functions that contribute to cancer progression remains poorly understood. Here, we demonstrate that protein kinase R-like endoplasmic reticulum kinase (PERK) activated by lipid deprivation or ER stress phosphorylates ADSL at S140, leading to an enhanced association between ADSL and Beclin1. Beclin1-associated ADSL produces fumarate, which in turn inhibits lysine demethylase 8-mediated Beclin1 demethylation, resulting in enhanced Beclin1 K117me2, subsequent disruption of the binding of BCL-2 to Beclin1 and elevated autophagy. Blocking the ADSL-Beclin1 axis by knock-in mutation or a cell-penetrating peptide inhibits autophagy induced by lipid deprivation and ER stress and blunts liver tumor growth in mice. Additionally, ADSL pS140-upregulated Beclin1 K117me2 levels are positively correlated with autophagy levels in human hepatocellular carcinoma specimens and poor patient prognosis. These findings uncover the function of ADSL in autophagy regulation and liver tumor development.