Abstract: In the present study, a new ceramide, namely 2S, 3R-4E, 8E-2-(heptadecanoylamino)-heptadeca-4, 8-diene-1, 3-diol ( 1 ), along with four known steroids, including 24-methylcholesta-5, 24(28)-diene-3β-ol ( 2 ), 24-methylcholesta-5, 24(28)-diene-3β-acetate ( 3 ), 4-methyl-24-methylcholesta-22-ene-3-ol ( 4 ), and cholesterol, was isolated and characterized from CH₂Cl₂/MeOH extract of Cespitularia stolonifera. A new acetate derivative of compound 1 , termed 2S, 3R-4E, 8E-2-(heptadecanoylamino)-heptadeca-4, 8-diene-1, 3-diacetate ( 1a ), was also prepared in the present study. All the structures were established on the basis of modern spectroscopic techniques, including FT-IR, 1D, 2D-NMR, HRESI-MS, and GC-MS, in addition of chemical methods. (-)-Alloaro-madendren, ledane, (1)-alloaromadendren oxide, isoaromadendrene epoxide and (-)-caryophellen oxide were identified from the n-hexane fraction using GC-MS. The extract and the two ceramides ( 1 ) and ( 1a ) exhibited significant cytotoxic activity against lung cancer A549 cells, while the extract and the two steroids ( 2 ) and ( 3 ) exhibited significant cytotoxic activity against breast cancer MCF-7 cells. The CH₂Cl₂/MeOH extract exhibited significant antiulcer activity in both ethanol and acetic acid induced ulcer models in rats, as evidenced by histopathological, histochemical, and biochemical examinations.