Tru Long pummelo is an endemic plant of Quang Nam province with high economic value. However, many different diseases, especially brown spot disease caused by Alternaria fungus on pummelos, have affected the quality of pummelos. Pesticides are overused and misused for the environment and human health. Therefore, there is an urgent need to reduce the use of synthetic chemicals. Biological control offers an alternative to the use of pesticides. Eight yeast strains have been isolated from healthy leaves, pummelo fruits, and healthy mulberries. They were screened for biological activity against Alternaria sp. by the dual culture method. The inhibitory potency ranged from 10.46% to 59.86%. The strain with the highest percentage (59.86%) was identified as Candida tropicalis using sequence analysis of the ITS region.