To further explore powdery mildew (caused by Golovinomyces cichoracearum) natural products, an extract from the fermentation of endophytic Aspergillus fumigatus was investigated. As a result, six isoindole alkaloid derivatives (1-6) were isolated. Among them, two compounds (1 and 2) were newly discovered and the activity evaluation of the purified compounds 1-6 against G. cichoracearum was studied. The results revealed that compounds 1-6 demonstrated obvious anti-G. cichoracearum activities for cigar tobacco in the range of 40.6% +/- 5.4 to 66.5% +/- 4.9 at a concentration of 250 mu g/mL, respectively. However, these rates are lower than that of positive control. By isolating and structurally identifying the above isoindole alkaloids, new materials conducive to improving the utilization of N. tabacum-derived fungi could be developed for screening anti-powdery mildew drugs.