Recently, de novo CYFIP2 variants have been identified in individuals with neurodevelopmental disorders and epilepsy. Considerable progress has revealed CYFIP2’s role as a component of the WAVE regulatory complex controlling actin cytoskeleton dynamics in neuronal development and function. However, its molecular functions remain partially unresolved. In our previous study, we unexpectedly discovered RNA-binding proteins (RBPs) among the CYFIP2 interactome from the neonatal mouse forebrain, suggesting that CYFIP2 may have novel functions in RNA regulation potentially mediated by these RBPs. However, the RNA-related function of CYFIP2 has not been investigated in detail. In this study, we revealed 278 differentially expressed proteins performing quantitative proteomic analysis on the forebrains of Cyfip2 knock-out (KO) embryonic mice and wildtype. Parts of these proteins were associated with membraneless organelles (MLOs) involved in mRNA processing and translation. Additionally, single-cell transcriptomic analysis of the Cyfip2 KO forebrain identified differentially expressed genes, linked to cellular stress responses and MLOs. We also observed morphological changes of MLOs in Cyfip2 KO brains and CYFIP2 knock-down (KD) cells under stress condition. Lastly, we demonstrated that CYFIP2 KD in HEK293T cells suppressed the phosphorylation levels of the alpha subunit of eukaryotic translation initiation factor 2 (eIF2α), enhancing protein synthesis, presumably by altering the G/F-actin ratio. Collectively, this study demonstrates the biological function of CYFIP2 is not restricted to actin dynamics but also extends to eIF2α phosphorylation and protein synthesis. With these dual functions, CYFIP2 may fine-tune the balance between MLO formation/dynamics and protein synthesis, critical for proper mRNA processing and translation.