Abstract:Alternaria rot of Pingguoli pear was a disease with latent infection character. Fruit surface showed sound within 60 days storage at cool condition (0℃, RH 85% -90%), black-gray hyphae could be seen in lenticels or calyx tube after 90 days storage, then tissues around lenticels collapsed and resulted in visible black spot. The incidence of Alternaria rot reached 28.86% at 100 days storage. The causal fungus isolated from the black spots was identified as Alternaria alternata(Fr.)Keissl. This pathogen was able to infect fruits through two pathways during pear growing season. The pathogenic fungus can colonize firstly on styles at blossoming stage and grow into carpel cavities gradually after 50 days of petal fall. The colonization of the pathogen could be 45% in carpel cavity till harvest time. It can also attack fruit surface and remained latent under epidermal cells during fruit development. The colonization of the pathogen at calyx end, middle part and stem end of fruit peel was 40%, 24% and 42.8% respectively at harvest time.