Safranal is a cyclic monoterpene which occurs in saffron (Crocus sativus). Gastric cancer is a highly prevalent malignancy worldwide, which is also among the five most common cancers in Iran. Although surgery, chemotherapy and radiotherapy are routine approaches for gastric cancer, the survival rate of patients at advanced stages is low. The purpose of current research was to study apoptosis-inducing effects of safranal and radiotherapy on human gastric cancer cells for the first time. To do so, MKN-45 cells were treated with 1.6 mM safranal for 96 h. Meanwhile, cells were treated with 1.6 mM safranal for 48 h, exposed to 6 Gy ionizing radiation and recovered for 48 h. Cells only exposed to 6 Gy radiation and recovered for 48 h were also considered in our study. To study changes induced on the cell cycle, treated cells were harvested and suspended in the staining solution containing propidium iodide (PI). For detection of apoptosis, cells were suspended in the binding buffer containing FITC-annexin V and PI and finally analyzed by flow cytometry. Our findings revealed that treatment of human gastric adenocarcinoma cells with safranal led to the accumulation of cells in the sub G1 phase of the cell cycle, and increased the number of early and late apoptotic cells. Likewise, treatment of cells with safranal + radiation also changed the distribution of cells in the cell cycle and increased the number of apoptotic cells. Radiation, however, did not induce considerable changes on MKN-45 cells. More research is suggested to determine the mechanism of safranal action on gastric cancer cells.