Psorergates rattus Fain & Goff, 1986 has been found in the brown rat Rattus norvegicus (Berkenhout, 1769) in Poland.The species has previously been found only once, in the tail base of the brown rat in the United States. In the present case, ten rats from two localities in Poland (Pomerania) were examined and infestation was discovered in 20% of them, with a total of 12 mites found. This is not only the first discovery of the species in Poland and the second globally, but also the first observation of representatives of Psorergatidae in rodents of the genus Rattus in Europe. Moreover, immature specimens of P. rattus have been observed for the first time.The infestation was asymptomatic, although in the earlier study mange was observed despite the relatively low density of the mites, which indicates a potential pathogenic threat not only to wild rat populations, but also to laboratory animals and pets.