[Objectives]  To report the biology of a new, economically important, invasive pest of the black locust Robinia pseudoacacia L, Chrysaster ostensackenella (Fitch, 1859), and a congeneric species, C. hagicola Kumata, 1961 of the family Gracillariidae in China. [Methods]  The damage on leaves of the black locust and the biology of these pests were studied in the field. [Results]  Chrysaster ostensackenella was recorded for the first time in China in Shandong and Liaoning Provinces. The record reported here is the only validated record of this species outside its native North American range. In Yantai, Shandong Province, C. ostensackenella had four generations a year and attacked more than 80% of the leaflets of black locust trees, resulting in an accelerated abscission of leaves. In some of the more seriously infested stands, all trees, and more than 90% of leaflets were damaged. In addition, a congeneric species, C. hagicola, was newly recorded in China, and its biology studied. Morphological and diagnostic characters of the two pests are provided to assist precise identification and biological monitoring. [Conclusion]  Both species of the genus Chrysaster Kumata are found in China, of which C. ostensackenella is an invasive pest that seriously threatens the black locust, R. pseudoacacia. Relevant control measures should be undertaken by afforestation and plant quarantine departments and intensive studies conducted to fully understand this invasive species.