Strain with valonia tannin resisting was isolated from nature and proved to be quite effective on biodegradation of valonia tannin.The optimum conditions for the degradation were pH 4.5 and 28 ℃ in 120 r/min for 8 days,which led to 64% COD removal rate of culture medium.The degradation rate of valonia tannin in culture medium was significantly increased by acclimatizing the strain.The effects of carbon and nitrogen sources and the ratio of carbon to nitrogen on biodegradation of valonia tannin were also investigated.Glucose takes advantage of the degradation.The highest biodegradation rate of valonia tannin in culture medium was achieved when the ratio of carbon and nitrogen was 10∶1 .It was also found that the higher ratio of carbon and nitrogen is more suitable for biodegradation of valonia tannin,and the higher nitrogen content obviously inhibits the degradation.