Fruit rot caused by Lasiodiplodia theobromae is one of the major diseases of longan. This study investigated the host range and reservoirs of the pathogen in longan farms of Ba Ria–Vung Tau, Viet Nam. A total of 32 fruits were identified as the hosts of L. theobromae. Among those, 20 fruits showed rot symptoms after pathogen inoculation. Besides the longan cultivars Xuong com vang, Long, Hung Yen, Edor and Tieu da bo, An Phuoc plum was highly susceptible to L. theobromae. Avocado, guava, rough orange, mandarin, rambutan, jackfruit, banana and sapodilla were moderately susceptible to the pathogen. Solanaceae and Cucurbitaceae fruits did not show clear symptoms after pathogen inoculation. Mycelia and pycnidia of L. theobromae could survive in inflorescence peduncles, fruit pedicels and dried fruit tissues which help the pathogen persist in longan farms through different cropping seasons. The pycnidia in these reservoirs release L. theobromae conidia, thus fostering continuous infection of fruit rot in longan farms.