Background Radiosurgery is increasingly used to treat vestibular schwannomas (VSs). Increasing the sensitivity of VS cells to irradiation (IR) could allow for lower and/or more effective doses of IR, improving safety and efficacy. Persistent JNK activity in VS cells reduces cell death by suppressing accumulation of reactive oxygen species (ROS) raising the possibility that JNK activity protects against IR-induced VS cell death, which is mediated by ROS. Objective Determine the extent to which JNK signaling contributes to VS cell radiosensitivity. Methods Primary human VS cultures, derived from acutely resected tumors, received single doses (5–40 Gy) of γ-irradiation. Histone 2AX phosphorylation, a marker of IR-induced DNA damage, was assayed by western blot and immunostaining. ROS levels were quantified by measuring 2',7'-dichlorodihydrofluorescein diacetate (CM-H2DCFDA) fluorescence. Cell apoptosis was determined by terminal deoxynucleotidyl transferase dUTP nick end labeling. Results The JNK inhibitors, SP6000125 and I-JIP, reduced H2AX phosphorylation following IR. They also increased H2DCFDA fluorescence in non-irradiated cultures and significantly increased IR-induced (5–10 Gy) H2DCFDA fluorescence 72 hours, but not 2 hours, after IR. Finally, I-JIP (50 µM) significantly increased VS cell apoptosis in cultures treated with 20–40 Gy. I-JIP (20 µM), SP600125 (20 µM), and JNK1/2 siRNA knock-down each increased VS cell apoptosis in cultures treated with 30–40 Gy, but not lower doses, of IR. Conclusions Inhibition of JNK signaling decreases H2AX phosphorylation and increases ROS and apoptosis in VS cells following γ-irradiation. These results raise the possibility of using JNK inhibitors to increase the effectiveness of radiosurgery for treatment of VSs.