In vitro, survival and function of rat pancreatic β-cells are optimally preserved in the presence of 10mmol/l glucose (G10) and markedly altered by prolonged culture at either 2mmol/l glucose (G2) or 30mmol/l glucose (G30). The increase in islet cell apoptosis in G2 and G30 vs. G10 is preceded by parallel increases in the mRNA levels of the integrated stress response (ISR) gene activating transcription factor 3 (Atf3) and its putative target and proapoptotic gene growth arrest- and DNA damage-inducible gene 153 (Gadd153/Chop). In this study, we used islets from Atf3 knockout (Atf3^−/−) mice to test the role of ATF3 in the stimulation of islet cell apoptosis under conditions associated with ISR activation. The glucose sensitivity of Atf3^−/− and WT islets for the stimulation of insulin secretion and Xbp1 mRNA splicing during 18h culture was similar, demonstrating that glucose metabolism was unaffected by Atf3 deletion. However, the stimulation of islet cell apoptosis by the SERCA pump inhibitor thapsigargin was slightly but significantly reduced in Atf3^−/− vs. WT islets despite similar level of expression of Gadd153 and Gadd34 mRNA. Also, the stimulation of islet cell apoptosis by 7days of culture in G2 was slightly but significantly reduced in Atf3^−/− vs. WT islets, and this effect was accompanied by a significant reduction in Gadd153 mRNA expression. In conclusion, the increase in Atf3 gene expression induced by thapsigargin and low glucose concentrations slightly contributes to the stimulation of islet cell apoptosis under these culture conditions.