The EFSA Panel on Plant Health performed a pest categorisation of Takahashia japonica (Hemiptera: Sternorrhyncha: Coccidae), the Asian string cottony scale, for the EU. This insect is native to Japan, and it is now established in many countries in Asia. It was first recorded in the EU (Italy) in 2017 and has also been found in Croatia. It is not listed in Annex II of Commission Implementing Regulation (EU) 2019/2072. It is polyphagous, feeding on broad-leafed trees and shrubs assigned to 25 genera belonging to 17 families. Host plant species commonly found in EU include maple (Acer spp.), alder (Alnus japonica), silkworm mulberry (Morus alba), black mulberry (Morus nigra), quince (Cydonia oblonga), walnut (Juglans regia), cherry plum (Prunus cerasifera), apple (Malus domestica) and citrus (Citrus sp.). Climatic conditions and availability of host plants in southern and central EU countries have allowed this species to establish and spread. Impact in cultivated hosts including citrus, mulberries, quinces, apples, plums, forest trees, as well as ornamental plants, is anticipated. Phytosanitary measures are available to reduce the likelihood of entry and further spread. T. japonica meets the criteria that are within the remit of EFSA to assess for this species to be regarded as a potential Union quarantine pest.