Mori fructus (Morus alba L., Morus, Moraceae) has been cultivated extensively for a long time in China. The fruit is delicious and beneficial for people’s health. In May 2016, a severe sour rot disease on the postharvest and ripe mulberry fruit was observed in the local fruit market of Chengyang district of Qingdao city (36°18′25.24″N, 120°23′28.17″E), Shandong province, China, which resulted in approximately 50% yield losses of fruits. The initial symptoms of the disease appeared as some small white mildew spots, which spread gradually and covered the whole fruit surface with a thin layer of white mycelium. The infected ripe fruit displayed a water-soaked soft rot with a sour odor. Twelve fungal isolates that showed similar morphological characteristics were isolated from the diseased fruits. Specimens were deposited in the Mycological Herbarium of Qingdao Agricultural University. Colonies plated on potato dextrose agar were white, flat, and nearly powdery. Mycelia were hyaline, septate, with 2.5 to 6.3 μm width and about 5.0 mm/day growth rate at 28°C, which were often extended by dichotomous branching. Arthroconidia, produced from long aerial chains, were achromatous, one-celled, cylindrical (5.0 to 15.0 × 3.5 to 6.3 μm), and germinated from one single end. Morphological characteristics matched the descriptions of Geotrichum candidum (De Hoog et al. 1986). To confirm the identification, genes of the internal transcribed spacer (ITS) using ITS1 and ITS4 primers, 26S rDNA, and the extensive factors (TEF-1α) were amplified. The resulting 295-bp sequence of ITS was deposited in GenBank (accession no. KY486783), which showed 99% similarity with Galactomyces geotrichum (accession no. AJ279445.1) and 98% similarity with G. candidum (accession no. JN974289.1). The resulting 588-bp sequence was obtained after the amplification of the 26S rDNA gene, which showed 99% similarity with G. candidum (GenBank: KY107740 and JN974268). A sequence of 281 bp (accession no. KY486781) was obtained after the amplification of TEF-1α (Ef728M and Tef1RX). It had 99% similarity with the TEF-1α gene (accession no. HF559206.1) of G. geotrichum strain CBS 772.71. Based on morphology and approaches of molecular biology, the pathogen was identified as G. candidum. Pathogenicity assays were confirmed by inoculating fresh mulberry fruit. Forty fruits were surface sterilized; among them, 20 fruits were inoculated with conidial suspension (10⁴ conidia/ml, 50 μL for each fruit), and the rest were treated with the same volume of sterilized distilled water for the control. All treatments were cultivated at 28°C. After 2 days of inoculation, white mildew spots appeared, and they spread quickly 5 days later. All inoculated fruits decayed to be liquid with a fermented smell 15 days later. The disease symptoms were the same as those naturally infected. The control fruit remained symptomless. This pathogen was reisolated from the infected fruits, whereas it was not isolated from the control. Therefore, it confirmed that G. candidum was the causal agent of the disease. G. candidum has been previously reported to cause sour rot of strawberry, loquat, and peach (Alam et al. 2017; Hafeez et al. 2015; Hussain et al. 2016), but this is the first report of G. candidum infecting mulberry fruit in China. This fungus detracted from the quality of the fruit and caused great economic losses.