A minor, sweet cucurbitane-glycoside, named iso-mogroside V (1), was isolated from Luo Han Guo (Siraitia grosvenorii (Swingle) C. Jeffery) along with five previously reported mogrosides. The structure of iso-mogroside V, 3-[(4-O-beta-D-glucopyranosyl-beta-D-glucopyranosyl)oxy]-mogrol-24-O-beta-D-glucopyranosyl-(1-->2)-O-[beta-D-glucopyranosyl-(1-->6)]beta-D-glucopyranoside, was established on the basis of extensive 2D-NMR (COSY, TOCSY, NOESY, HSQC, and HMBC) and LCMS analyses. The five known mogrosides were identified as mogroside V (2), 11-oxo-mogroside V (3), siamenoside I (4), mogrosides IVa (5) and IVe (6). Iso-mogroside V was determined to be approximately 500 times sweeter than 0.5% (w/v) sucrose.