Two new glycerides, didemnacerides A (1) and B (2), together with three known sterols, 24-ethyl-25-hydroxycholesterol (3), cholest-6-en-3,5,8-triol (4) and cholestane-3,5,6-26-tetrol (5), were isolated from the Red Sea ascidian Didemnum sp. Their structures were elucidated by using extensive 1D (1H, 13C) and 2D (1H–1H COSY, HSQC and HMBC) NMR studies and mass spectroscopic data (GC-MS and HR-MS) as well as alkaline hydrolysis followed by GC–MS and NMR spectral analyses of the fatty acid methyl esters. This is the first report of compounds 3–5 from the Red Sea ascidian Didemnum species.