Temozolomide (TMZ) therapy exert limited clinical benefits in glioblastoma multiforme (GBM) patients with high EGFR activity, underscoring the need for effective combination therapy. Here, we show that tonicity-responsive enhancer binding protein (NFAT5) lysine methylation, is a determinant of TMZ response. Mechanistically, EGFR activation induces phosphorylated EZH2 (Ser21) binds to and triggers NFAT5 methylation at K668. Methylation prevents NFAT5 cytoplasm interaction with E3 ligase TRAF6, thus blocks TRAF6 induced K63-linked ubiquitination mediated NFAT5 lysosomal degradation and cytosol localization restriction, result in NFAT5 protein stabilization, nuclear accumulation and activation. Methylated NFAT5 leads to the upregulation of ITGB1, a transcriptional target of NFAT5, which is responsible for unfavorable TMZ response. Inhibition of NFAT5 K668 methylation improved TMZ efficacy in vivo. Notably, NFAT5 K668 methylation levels are elevated in TMZ-refractory specimens and confer poor prognosis. Our findings suggest targeting NFAT5 methylation as an effective therapeutic strategy to improve TMZ response in tumors with EGFR activation.