Black spot is one of the most destructive diseases of roses, causing premature defoliation, thus progressively weakening the plant and even leading to death. This study aimed at identifying the pathogen causing black spot on Rosa chinensis Jacq. cv. nhung (Hồng Nhung) and R. chinensis Jacq. var. minima (Hồng Tỉ Muội) in Sa Đéc city, Đồng Tháp province, Vietnam, using a combination of conidia morphology and pathogenicity tests including detached leaf and intact plant techniques. A total of 32 infected leaf samples with the black spot typical symptoms were collected from six rose cultivation areas. The morphological characterization of the conidia obtained from these samples was elliptical, hyaline, two-celled and had vacuole-like structures, similar to those produced by Diplocarpon. In pathogenicity test, the symptoms were observed on cv. nhung but not var. minima in the detached leaf technique while symptoms were observed on both cultivars in intact plants technique. These included black spots with perforated edges, aggregating into bigger patches. The infected leaves could yellow and defoliate at 21 days after inoculation. Compared to the previous pathogenic studies and description of diseases on roses, the fungal pathogen was identified as fungus Diplocarpon rosae.