Abstract: To identify the pathogenic fungi responsible for mildew in fermented cigar tobacco leaves from Chenzhou City, Hunan Province, 48 fungal strains were isolated and purified by tissue culture method, among which Aspergillus sp. (20.83%) and Penicillium sp. (20.83%) accounted for the highest proportion. The cultivable fungi in the fermented cigar tobacco leaves were identified by morphological and molecular biological methods, and the mildew-causing ability of 12 representative fungi was determined according to Koch's postulate. Strain CX15, identified as Penicillium citrinum, and strain CX35 as Aspergillus insulicola, were found to have strong mold-causing ability on cigar tobacco. The results of the culture temperature and relative humidity tests showed that strains CX15 and CX35 could grow in the temperature range between 25-40 ℃, and the optimal growth temperature was 30 ℃. They could grow in the relative humidity range of 50%-90%. When the relative humidity was 90%, strain CX15 grew the fastest, and when the relative humidity was 80%, strain CX35 grew the fastest.