Ultraviolet radiations exist in the sunlight which is harmful for human health. UVB (280-315nm) radiation is considered to be a carcinogen, and UVA (315-400nm) may be the primary cause of sunlight-induced melanoma because of generation of reactive oxygen species (ROS). Nowadays, the use of sunscreencontaining effective UV filtering agentsis the most common UV protective method. However, there are huge demand of novel sunscreenswhich are composed of natural substances without synthetic chemicals and minerals. Lichens are considered a great bio-resource because they produce large numbers of secondary metabolites with many biological activities,such as antioxidant activity, antimicrobial activity, and anticancer activity.Lichen could survival in strong sunlight condition without damage, the reason may be there are some substance existed in lichen thallus can absorb UV radiation for avoiding damage. Therefore it is a high probability to get UV absorption substances from whose habitat is intensive UV radiation regions.In chapter Ⅱ, weinvestigated the lichen species growing on rocks exposed to high intense of sun light in highland of Yunnan and arid area of Xinjiang province, China, for screening UV absorption active substances. Preliminary results showed there were 19 species of lichencrude extracts exhibiting strong absorption activity inUVB region and two crude extractsisolated from lichens: Cetrariopsis wallichianaand Flavocetraria cucullata, which have both UVB and UVA absorption activities.Based on color and Rf value of the spots on TLC plate, combine retention time and UV spectra of substance peak in HPLC results compared with database of lichen substance to match compounds, the UV absorption active lichen substances were identified.Interestingly, the major UV absorption active substances in C.wallichianaand F.cucullatawere same. The lichen substance which possessed UVB absorption activity was identified as usnic acid and another one was regarded as secalonic acid Awhich could absorbs UVA. Antioxidant activities of 21 samples of lichen crude extracts were determined by four in vitroassays. Antioxidant activity of Secalonic acid A was high than that of usnic acid. Remarkably, the cytotoxicity of these two crude extracts of C.wallichiana and F.cucullatawere muchhigher than other lichens against mouse melanoma cell line, B16F1 and B16F10, and normal cell, HaCaT, which was because the high cytotoxic activity of secalonic acid A. The low IC50valuesof secalonic acid A suggested it might be a good anticancer agent against B16F1 and B16F10 cells, unfortunately, it exhibited high cytotoxicity against HaCaT cell.A disadvantage of lichen is that they have not been cultivated under artificial conditions to date. As a result, lichen substances from natural sources are limited and have not been widely utilized in commercial applications. Accordingly, interest in lichen-associated fungi, especially endogenic fungi, has increased. In chapter Ⅲ, we purified (3R)-5-hydroxymellein, which has UVA absorption activity, from the secondary metabolites of an endolichenic fungus (EL000039). The antioxidant properties were then assessed by in vitro tests. The antioxidant activity of (3R)-5-hydroxymellein was high when compared to the recognized antioxidants ascorbic acid (ASA) and butyl hydroxyl anisole (BHA). Moreover, the compound exhibited no cytotoxicity toward the mouse melanoma cell lines, B16F1 and B16F10, or the normal cell line, HaCaT. Furthermore, (3R)-5-hydroxymellein recovered the damage caused by UVB irradiation and inhibited melanin synthesis. Taken together, these results suggest that (3R)-5-hydroxymellein could be a multifunctional potential UV protective agent byin vitrotests. Finally, the PDB medium was optimal for yield of (3R)-5-hydroxymelleinproduced by endolichenic fungusunder the optimal culture conditions which were at 25℃, medium PH 4.5-6.0 and 21 days period. In chapter Ⅳ, 7-hydroxy-2-octenoic acid-ethyl esterhas UVA absorption activity,whichwas purifiedfrom the secondary metabolites of anotherendolichenic fungus (EL000548). The antioxidant properties were performedby in vitrotests. The superoxide anion scavenging activity and inhibition of linoleic acid peroxidation of 7-hydroxy-2-octenoic acid-ethyl esterwas higherthan ASAand BHA. Moreover, the compound exhibited no cytotoxicity toward the mouse melanoma cell lines, B16F1 and B16F10, except forthe normal cell line, HaCaT. 7-hydroxy-2-octenoic acid-ethyl esterrecovered the damage caused by UVB irradiation and inhibited melanin synthesis. In conclusion, 7-hydroxy-2-octenoic acid-ethyl estercould be anothermultifunctional potential UV protective agent byin vitrotests.