Temozolomide (Tmz) faces the challenges of high chemoresistance and high dose leading to various side-effects. Chrysin exhibits anticancer and adjuvant effects in various cancer models. Nevertheless, chrysin’s synergistic effect with Tmz against Tmz-sensitive and Tmz-resistant human glioblastoma has never been reported. Chrysin and Tmz reduced the viability of A172 and LN18 in concentration- and time-dependent manner, with chrysin exhibited IC50 values lower than Tmz. The combination of chrysin and Tmz enhanced cell death (CI indexes between 0.59–0.98), suggesting synergistic efficacy of chrysin at lower concentrations. Chrysin promoted Tmz-induced phosphatidylserine externalization and depolarization of mitochondrial membrane potential. Chrysin promoted Tmz-induced suppression of pAkt (Ser473) and pERK1/2 (Thr202/Tyr204) while enhanced the phosphorylation of p38 MAPK (Thr180/Tyr182). This further reduced the antiapoptotic proteins (Bcl-2, Bcl-xL, Mcl-1), elevated proapoptotic proteins (Bax, Bad, Bak, PUMA, Noxa), and activated caspase-9 and caspase-3 compared to Tmz treatment alone. Pretreatment with Z-LEHD-FMK and Z-VAD-FMK attenuated apoptosis and restored caspase-9 and − 3 levels. However, pretreatment with Z-IETD-FMK did not suppress the promotion of apoptosis. Collectively, chrysin promotes Tmz-induced apoptosis through p38 MAPK activation and suppression of Akt and ERK1/2. These results suggest chrysin as a potential therapeutic adjuvant to improve Tmz effects in Tmz-sensitive and -resistant GBM.