The stable carbon and nitrogen isotope technology is an effective method to study the structure and dynamics of food webs and trophic relationships in ecosystems. The stable carbon and nitrogen isotopes (δ¹³C and δ¹⁵N) are used to investigate food web and trophic relationships of the Guangxi Dongfeng Cave in this study. The Dongfeng cave located in Fuwang Village, Putao Town, Yangshuo County, Guangxi Province was investigated in July 2007. In this cave, 13 animal samples and 3 soil samples were collected for estimation of δ¹³C and δ¹⁵N. The results indicated the great range of δ¹³C values from -19.83‰ (Pholcus crypticolens) to -27.27‰ (Sypna picta). The samples of Pholcus crypticolens and Steatoda phalerala have higher δ¹³C values than other spider groups, since the food source of the two species contains other insects. The range of δ¹⁵N value is from 2.62‰ (soil organic matter) to 5.64‰ (Geophiidae). The enrichment of δ¹⁵N in the food-web is more obvious than that of δ¹³C. For example, the different value of δ¹⁵N between diplopod and soil organic value is 1.16‰, and the difference of δ¹⁵N value Distrammena sp. and Sypna picta from soil organic matters is from 1.24‰ to 1.36‰. The gnawer food chains take a main role in the Dongfeng cave, because there is no illumination and plant in the dark area of the cave, and the soil organic matters is the main carbon sources as the first trophic level. The mainly prey relations are diplopod or snails to soil organic matters etc. In the ecosystem of this cave, 3 species of diplopod are the primary consumers, and the difference value (2.04‰) between Tegettaria sp. and other diplopods is the enrichment ratio of the stable nitrogen isostope of the food-web in Dongfeng cave. According to trophic model, the primary consumers are soil animals (such as diplopod groups, and Opeas gracile), Sypna picta, and Distrammena sp., as the second trophic level (that is the primary consumers). The third trophic level includes spiders groups, Systenocentrus sp., Geophiidae, and Bufo mdanostictus as the secondary consumers. The composition of δ¹³C and δ¹⁵N or the enrichment ratios to δ¹⁵N at all levels of consumers in the karst caves are generally lower than those in the earth surface ecosystem where on the composition and the enrichment ratio of δ¹⁵N, Passer montanus in Maduo County of Qinghai Province has (7.77±0.53)‰, Macrobrachium nipponense and Carassius auratus in Xingzi County of Jiangxi Province (14.3±0.5)‰ and (10.8±0.9)‰ respectively. Their average enrichment ratio of δ¹⁵N among different trophic levels of the earth surface ecosystem is (3.4±1.1)‰. In the Dongfeng cave, however, the highest value of δ¹⁵N is Geophiidae (5.64‰), and the enrichment ratio of ecosystem is only 2.04‰. Its reasons of low enrichment may be the effect of food source and life metabolism on δ¹⁵N of living beings in karst caves where there are poor food, small life body, low oxygen consumption, and low metabolic process.