The thin-layer chromatographic analysis of the crude oligosaccharides extracted from yacon revealed the presence of glucose, fructose, sucrose, 1-kestose and nystose. The qualitative and quantitative analysis was carried out on oligosaccharides by high pressure liquid chromatography and the results showed that the contents of d-glucose, fructose, sucrose, 1-kestose, nystose and 1-fructofuranosyl nystose in oligosaccharides were 38.30%, 16.44%, 14.58%, 12.29%, 12.17%, 6.20%, respectively. The content of the fructooligosaccharides in oligosaccharides was 30.66%. The crude oligosaccharides were separated and purified by silica gel column chromatography. The two fractions obtained from crude oligosaccharides were 1-kestose and nystose, which were identified by mass spectra. The yield of 1-kestose and nystose were 10.36% and 9.73%, respectively. The purity of 1-kestose was 82.9% and of nystose was 73.6%.