Potato (Solanum tuberosum L.) is an important crop throughout the world. An uncharacterized disease has been observed on potato plants during the growing season and tubers during the storage period from Nileke County, Qitai County and other locations in Xinjiang, China. A particular fungus was consistently isolated from the infected potato plants and tubers. Based on its morphology, molecular characteristics, pathogenicity test and internal transcribed spacer (ITS) sequence, the pathogens was identified as Galactomyces candidum F12. Further study also showed that the hyphae and conidia of the pathogenic fungus grew faster as the temperature was 30°C, pH was 7, soluble starch was used as optimal carbon source and yeast powder as optimal nitrogen source. In addition, 12-h continuous illumination light was beneficial to the hyphal growth, while 24-h continuous illumination was beneficial to the sporulation of the strain at 30°C. To our knowledge, this is the first report of Galactomyces candidum causing leaf wilt and postharvest tuber rot on potato in China.