[Background] In July to August 2018, anthracnose of lettuce occurred in a large area of Wushengyi town, Yongdeng county, Lanzhou city, Gansu province, China. About 40% fields suffered from the disease, and 10% fields failed to harvest. [Objective] Identify the pathogen of anthracnose on lettuce. [Methods] Pathogen isolation was carried out by means of diseased tissue isolation method. Koch’s rule was used to prove the pathogenicity of fungal strain isolated from lettuce. Morphological and molecular biological methods were used to identify the pathogen. [Results] Three fungal strains with similar morphological characteristics, were isolated from diseased samples. Conidia fusiform, with one septum, slightly curved, (10.44?19.40) μm×(2.61?4.48) μm, when the pathogen was cultured on PDA medium for 7 d at 20 °C. Artificial inoculation with representative strain Lett-11 on detached lettuce leaves, induced symptoms similar to in field. BLASTn analysis showed that the ITS sequences of strain Lett-11 (GenBank accession No. MK252097) had a 99% homology with Marssonina panattoniana strain CBS 163.25 (GenBank accession No. MH854831.1). [Conclusion] Pathogen causing anthracnose on lettuce was identified as Marssonina panattoniana [Synonymy: Microdochium panattonianum]. This is the first report of anthracnose of lettuce caused by Mar. panattoniana in Gansu province, China.