Phosphorylation of PBL19 mediated by CERK1 in response to chitin is crucial for enhancing plant defense against fungal pathogens, underscoring the importance of chitin signaling in plant immune responses. Fungal pathogens pose a serious threat to global agriculture, causing substantial yield losses. Plants have evolved complex defense mechanisms, including the recognition of chitin, a major component of fungal cell walls, to activate immune responses that are crucial for defense against pathogens. Protein phosphorylation plays a pivotal role in regulating these responses, fine-tuning immune signaling pathways. Here, we investigate PBL19, a member of the RLCK VII subfamily in Arabidopsis thaliana, known for its pivotal role in chitin signaling pathways. Our study reveals that upon chitin perception, PBL19 undergoes phosphorylation-mediated by the receptor CERK1. Through mass spectrometry analysis, we identified eight specific phosphorylation sites on PBL19. Functional characterization revealed their crucial role in enhancing fungal resistance mechanisms in plants. This study advances our understanding of how plants employ phosphorylation-mediated signaling to combat fungal pathogens, providing insights into fundamental mechanisms of plant immunity.