To investigate the sweet-tasting components in the roots of Myriopteron externum, the phytochemical study of its roots was conducted, which led to the discovery of 12 new C21 pregnane glycosides (extensumside M-X, 1 - 12) and two known ones (extensumside C and extensumside E, 13-14). Their chemical structure elucidation was accomplished by means of spectroscopic methods: IR, UV, ESI-MS, and NMR (H-1 NMR, C-13 NMR, HSQC, H-1-H-1 COSY, HMBC, HSQC-TOCSY, and ROESY), as well as the chemical evidence. Sensory analysis of these compounds revealed that nine of them (l, 3, 4, 5, 6, 7, 8, 13, and 14) are highly sweet-tasting compounds. Their sweetness intensities are 25 to 400 times greater than that of sucrose. Analysis of the structure-activity relationship (SAR) indicated that the sweet intensities of the isolated compounds are closely related to the aglycone 3 beta,l6 alpha-dihydroxy-pregn-5-en-20-one, the number and type of the monosaccharide m the sugar chain linked to C-3 and C-16 and the position of the mBe group.