Drug-induced liver injury (DILI) is the leading cause of acute liver failure and poses a significant clinical challenge in both diagnosis and treatment. Serine synthesis pathway (SSP) links glycolysis to one-carbon cycle and plays an important role in cell homeostasis by regulating substance synthesis, redox homeostasis and gene expression. However, the regulatory mechanism of SSP in DILI remains unclear. Phosphoglycerate dehydrogenase (PHGDH) is the rate-limiting enzyme in SSP. Here we show that during DILI, mitogen-activated protein kinase 13 (MAPK13) is activated and then phosphorylates PHGDH at serine 371 upon oxidative stress, which triggers PHGDH protein degradation via chaperone-mediated autophagy (CMA) pathway. PHGDH degradation suppresses SSP and glutathione production, thereby exacerbating DILI and cholestatic liver injury. Importantly, both MAPK13 inhibition and dietary serine supplementation ameliorates these liver injuries. Our finding demonstrates a unique regulatory mechanism of SSP, in which MAPK13 phosphorylates PHGDH and promotes its CMA degradation, establishes its critical role in DILI and cholestatic liver injury, and highlights the therapeutic potential of MAPK13 inhibitor or dietary serine to treat these liver injuries.