The non-coding transcriptome, in particular microRNAs (miRNA), influences cellular survival after irradiation. However, the underlying mechanisms of radiation-induced miRNA expression changes and consequently target expression changes are poorly understood. In this study, we show that ionizing radiation decreases expression of the miR-23a~27a~24-2 cluster through transcriptional regulation by promoter methylation and at the post-transcriptional level by reduced processing through AGO-phosphorylation. Furthermore, we demonstrate that all three mature cluster miRNAs reduce apoptosis by increasing expression of the common target protein XIAP. These findings link a temporal succession of transcriptional and post-transcriptional regulatory mechanisms of the miR~23a~24-2~27a cluster, enabling a dynamic stress response and assuring cellular survival after radiation exposure.