Abstract: Objective:The aim of this study was to identify fungus species capable of converting caffeine to theophylline,and to provide strain to develop high-thephylline tea. Methods:With caffeine-agar solid selective medium,2 potential strains were screened out,and colony characteristics and conidial structure were identified by sequence determination of 18SrDNA. Based on liquid mediums with different concentrations of caffeine,tea soup submerged fermentation and tea-leaves solid-state fermentation,the ability of conversion from caffeine to theophylline of potential strains were studied. Results:Potential strains were identified as Aspergillus niger NCBT110A and Aspergillus sydowii NRRL250. The secondary screening in liquid-state cultivation with caffeine showed that caffeine utilization of A. niger NCBT110A was restrained,A. sydowii NRRL250 could convert caffeine to theophylline. In a certain caffeine concentration,caffeine degradation rate of A. sydowii NRRL250 was beyond 90% and more than half of caffeine was converted to theophylline.Tea soup submerged and sun-dried tea solid-state fermentation of A. sydowii NRRL250 showed that caffeine decreased significantly and theophylline increased sharply during A. sydowii NRRL250 fermentation(p<0.05). The caffeine degradation rates were 85.43% and 87.37%,theophylline reached(501.2±13.55) mg/L and 3.3293%±0.2463%(w/w),respectively. In the presence of caffeine,A. sydowii NRRL250 could convert caffeine to theophylline sharply. Conclusion:A. sydowii NRRL250 could convert caffeine to theophylline,which provided excellent strain to develop high-thephylline pu-erh tea or tea drinks.