It was established that .alpha.-spinasterol (I) was isomerized by hydrogen chloride to a mixture of two isomers. These isomers were separated into each of components and identified as .DLETA.$^{8(14),22}$ -stigmastadienol (III) and ${delta}$$^{14,22}$ -stigmastadienol (IV), respectively. The mass spectra of these compounds were found to be particularly suitable to idetify the position of nuclear double bond of sterols possessing 22 : 23 -double bond in side chain.