βketoacylACP synthase II (KASII)is a key enzyme responsible for the conversion of palmitic acid (16〖DK〗∶0ACP)to stearic acid (18〖DK〗∶0ACP). KASII activity determines the level of C18 fatty acids. In this paper, Dunaliella salina was used to isolate and identify the DsKASII gene. Bioinformatics tools were used to analyze the subcellular localization, protein structure, physicochemical properties and phylogenetic characteristics of DsKASII enzyme. Detail examinations were conducted for DsKASII gene expression pattern, oil/fatty acid profiles, the contents of chlorophyll and βcarotene under nitrogen deficiency stress. The results showed that  Dunaliella salina DsKASII enzyme protein had a length of 476 aa and a theoretical isoelectric point of 6.99. The protein contained plastidtargeting peptide and many hydrophilic regions. The main secondary structures included αhelix (22.48%), βsheet (22.06%), and random coil (55.46%). The 3D structure simulation predicted that the DsKASII was compactly heartshaped structure on the whole, with a homodimer as the functional form. Phylogenetic analysis indicated that DsKASII protein has the highest homology with Chlamydomonas reinhardtii CrKASII by 99%. It is possible that the two microalgae have a common evolutionary ancestor. Quantitative RTPCR (qRCPCR)analysis revealed that the expression level of DsKASII gene was upregulated in algal cells under nitrogen deficiency stress compared with the normal culture controls. The expression level of DsKASII in the stressed cells was 4.5 times higher than that in the normal culture cells on the 3th day of cultivation. Moreover, under nitrogen stress, the total oil, oleic acid (C18〖DK〗∶1)and carotenoid content in algae cells increased significantly, whereas palmitic acid (C16〖DK〗∶0)and chlorophyll contents decreased. Taken together, the data indicated that nitrogen stress induced the upregulation of DsKASII gene in Dunaliella salina, and then DsKASII catalyzed more palmitic acid into stearic acid, eventually increasing the accumulation of monounsaturated oleic acid and carotenoids. The present study provides a scientific reference for the further analysis on the mechanism underlying accumulation of oil and carotenoids as well as algal response to the stress, benefiting the breeding of highquality oleaginous microalgae.