The Chinese mitten crab ( Eriocheir sinensis) is a vector of the fatal crayfish plague pathogen (Aphanomyces astaci). Both species are listed among the worlds 100 worst invasive species. From its origin in China the Chinese mitten crab was introduced to Europe, presumably via ballast water from ships. A. astaci originated in North America and is assumed to have been firstly introduced to Europe through human- mediated transportation of live specimens of North American freshwater crayfish species. While the North American crayfish species are resistant to the pathogen, it causes a fatal disease to native European crayfish species. It was generally assumed that the crayfish plague could only infect freshwater crayfish species. Until recently, the Chinese mitten crab had not been recognised as a host of the pathogen. And no study has yet been carried out to investigate if they also serve as a vector. In this study, transmission experiments are carried out in combination with subsequent species-specific molecular analysis. The results establish that the Chinese mitten crab carry the crayfish plague pathogen and can transmit it to the European noble crayfish (Astacus astacus). The implications of these findings are ecologically alarming, considering the high invasive potential and the catadromous life cycle of Chinese mitten crabs, facilitating the widespread distribution of the pathogen.