<p>Hypoxia has been reported to induce high expression of HIF-1α in multiple cancer tissues, and HIF-1α significantly influences cancer progression, including gastric cancer (GC). However, the mechanism of HIF-1α in the GC process is not clearly elucidated. HIF-1α and JMJD3 expressions in GC tissues were first determined by qRT-PCR and western blot. Meanwhile, the prognosis of HIF-1α, and the relationship between HIF-1α and JMJD3 were analyzed through bioinformatics. Then, we silenced HIF-1α, knocked down or overexpressed JMJD3, or treated gamma-secretase inhibitor (DAPT) in GC cells under hypoxic conditions. Cell proliferation, apoptosis, and Notch activation was determined both in vivo and vitro. We initially proved that both HIF-1α and JMJD3 were highly expressed in GC tissues, high expression of HIF-1α was associated with a poor prognosis. Functionally, we observed that HIF-1α knockdown attenuated GC cell proliferation and enhanced apoptosis under hypoxic conditions, while JMJD3 knockdown exerted the opposite effect in hypoxia-induced GC cells. Besides, JMJD3 overexpression promoted proliferation and reduced apoptosis by upregulating Notch in GC cells under hypoxia conditions. Furthermore, HIF-1α knockdown inhibited tumor growth and altered the pathological structure in the tumors of GC model nude mouse. In GC cells, HIF-1α knockdown inhibited cell proliferation and promoted apoptosis by affecting JMJD3/Notch axis. Therefore, we demonstrated that HIF-1α/JMJD3/Notch axis might be a new therapeutic target for GC.</p>