Mulberry leaf (Folium mori) is the exclusive forage of silkworms, but also is an important traditional Chinese medicine widely used in China and some other countries. It shows so many pharmacological activities such as hypoglycemia, antioxidative, antineoplastic, antibacterial, antiinflammatory, et al. Much attention has paid to the chemical constituents research of mulberry leaves. And several compounds including flavonoids, alkaloids, phenylpropanoids and steroids have been isolated in recent years.China is the largest producer of mulberry and silk in the world. In China, there are 15 species and 4 varieties of the genus Morus. Mulberry is distributed all over the country. The area of mulberry field is about 752 713 ha. in 2004. And the mulberry leaves production is about 15 000 000 tons every year. In order to promote the development and industrialization of comprehensive utilization of mulberry leaves, the secondary metabolites of mulberry leaves were studied systematically.Column chromatographic techniques were used for isolation and purification, and spectroanalysis was used for structure identification, after extraction with solvent. 21 compounds were isolated from the leaves of Morus alba, 16 of which were identified as kaempferol-3-O-β-D-glucopyranoside (MOA-1), quercetin-3-O-β-D-glucopyranoside (MOA-2), 5, 7, 2', 4'-tetrahydroxyflavone-7-O-β-D-glucopyranoside (MOA-3), β-sitosterol-3-O-β-D-glucopyranoside (MOA-5, 18), β-sitosterol (MOA-6), benzoic acid (MOA-7), 7-hydroxycoumarin (MOA-8), uridine (MOA-9, 15), butanedioic (MOA-10, 13), kaempferol-3-O-(6"-O-2-butenoyl)-β-D-glucopyranoside (MOA-11), thymine (MOA-12), 7-Hydroxy-6-methoxy-coumarin-7-O-β-D-Glucopyranoside (MOA-14), D-galactitol (MOA-16), kaempferol-3,7-di-O-β-D-gluco-pyranoside (MOA-19), 5, 7-dihydroxycoumarin-7-O-β-D-glucopyranoside (MOA-23) and 3, 4-dihydroxy-benzoic acid (MOA-24). Among them, compound MOA-1, 2, 3, 11 and 19 are flavonoids, MOA-8, 14 and 23 are coumarins, MOA-5 (18) and 6 are steroids, MOA-7, 10 (13) and 24 are organic acids, MOA-9 (15) and 12 are N-containing compounds. MOA-7, 9 (15), 11, 12, 16, 19 and 24 were isolated from the genus Morus for the first time, MOA-3 is a new natural product, and MOA-23 is a new compound.The total flavonoid content (TFC) of mulberry leaves from different seasons, species and varities were determined with spectro photometry, after extracted with methanol. The differences of the TFC of different species were analysed for the first time. The result showed that, 1) the TFC of Yu 71-1 in autumn was significantly higher than that in spring and summer, and the content in October (before frost) was slightly higher than that in November (after frost). But there were no significant differences found in the TFC of Shigu 11-6 in spring and autumn. 2) The differences of the TFC among different species were very significant. The TFC of Morus wittiorum and Morus cathayana were higher than that of all other species very significantly, and the TFC oi Morus alba was very significantly lower than all other species. 3) Much variation was seen in TFC of the germplasms from Morus cathayana. Baojing 4 had the highest content (71.67 mg/g), and Dejiang 15 had the lowest (44.56 mg/g) content of total flavonoid. The range of TFC among Morus cathayana wasn't so wider than that among different species, except that Baojing 4 was very high. The TFC of Morus cathayana germplasms from the same habitat were similar. 4) Much variation was