A previously unknown bark beetle species, Acanthotomicus sp., has emerged as a lethal pest of American sweetgum (Liquidambar styraciflua) in China. Our survey of nursery records from around Shanghai suggests that American sweetgum have been under heavy attack since at least 2013, resulting in the death of > 10,000 trees. Mass attacks of the apparently sweetgum-specific Acanthotomicus sp. can be diagnosed by accumulation of resinous exudates on the trunk, wilted foliage, and eventual numerous exit holes of the new generation. A Chinese native sweetgum Liquidambar formosana can also be colonized by Acanthotomicus sp. This pest is of concern not only as a killer of sweetgum in the Chinese nursery trade but also as a potentially destructive invasive pest of sweetgum in North America. This discovery suggests that global preinvasion assessment of pests is warranted.