Anticancer drug gefitinib causes inflammation-based side effects, such as interstitial pneumonitis. However, its mechanisms remain unknown. Here, we provide evidence that gefitinib elicits pro-inflammatory responses by promoting mature-interleukin-1β (IL-1β) and high-mobility group box 1 (HMGB1) release. Mitochondrial reactive oxygen species (mtROS) driven by gefitinib stimulated the formation of the NLRP3 (NACHT, LRR and PYD-containing protein 3) inflammasome, leading to mature-IL-1β release. Notably, gefitinib also stimulated HMGB1 release, which is, however, not mediated by the NLRP3 inflammasome. On the other hand, gefitinib-driven mtROS promoted the accumulation of γH2AX, a hallmark of DNA damage, leading to the activation of poly (ADP-ribose) polymerase-1 (PARP-1) and subsequent active release of HMGB1. Together our results reveal the potential ability of gefitinib to initiate sterile inflammation via two distinct mechanisms, and identified IL-1β and HMGB1 as key determinants of gefitinib-induced inflammation that may provide insights into gefitinib-induced interstitial pneumonitis.