Background: Wild jujube (Ziziphus jujuba var. spinosa) exhibits remarkable tolerance to saline-alkali stress, yet its molecular mechanisms remain poorly understood. 3-ketoacyl-CoA synthase (KCS) is a key enzyme involved in the biosynthesis of very-long-chain fatty acids (VLCFAs), which constitute pivotal precursors for membrane lipids involved in stress adaptation. Methods: Through genome-wide analysis and molecular biology techniques, 20 ZjKCS genes were identified. Results: The ZjKCS genes were grouped into nine subfamilies, exhibiting highly conserved gene structures, motifs, and functional domains within each subfamily. Two pairs of collinear gene pairs were identified, with the ZjKCS12-ZjKCS18 pair retaining core conserved functions despite intense purifying selection. ZjKCS genes are rich in cis-acting elements associated with light transduction, phytohormone responses, and abiotic stress adaptation. Tissue-specific expression patterns of ZjKCS under light, ABA (abscisic acid), and MeJA (methyl jasmonate) treatments were analyzed by quantitative real-time PCR (qRT-PCR). Under saline-alkali stress, ZjKCS genes were significantly upregulated, with most showing strong sustained induction during later treatment stages. Conclusions: These findings indicate that the ZjKCS family participates in saline-alkali stress and abiotic stress adaptation, potentially by enhancing VLCFA synthesis to reinforce and remodel membrane lipid structure. This study provides a foundation for elucidating lipid-mediated stress resistance mechanisms in stress-tolerant fruit trees.