AbstractBASIC PENTACYSTEINE (BPC) transcription factors are essential regulators of plant growth and development. However, BPC functions and the related molecular mechanisms during cucumber (Cucumis sativusL.) responses to abiotic stresses, especially salt stress, remain unknown. We previously determined that salt stress inducesCsBPCexpression in cucumber. In this study,Csbpc2transgene-free cucumber plants were created using a CRISPR/Cas9-mediated editing system to explore CsBPC functions associated with the salt stress response. TheCsbpc2mutants had a hypersensitive phenotype, with increased leaf chlorosis, decreased biomass, and increased malondialdehyde and electrolytic leakage levels under salt stress conditions. Additionally, a mutatedCsBPC2resulted in decreased proline and soluble sugar contents and antioxidant enzyme activities, which led to the accumulation of hydrogen peroxide and superoxide radicals. Furthermore, the mutation toCsBPC2inhibited salinity-induced PM-H+-ATPase and V-H+-ATPase activities, resulting in decreased Na+efflux and increased K+efflux. These findings suggest that CsBPC2 may mediate plant salt stress resistance through its effects on osmoregulation, reactive oxygen species scavenging, and ion homeostasis-related regulatory pathways. However, CsBPC2 also affected ABA signaling. The mutation toCsBPC2adversely affected salt-induced ABA biosynthesis and the expression of ABA signaling-related genes. Our results indicate that CsBPC2 may enhance the cucumber response to salt stress. It may also function as an important regulator of ABA biosynthesis and signal transduction. These findings will enrich our understanding of the biological functions of BPCs, especially their roles in abiotic stress responses, thereby providing the theoretical basis for improving crop salt tolerance.