Abstract: In September 2021,the goldfish (C.auratus) cultured at two adjacent ornamental fish farms in Tongzhou District of Beijing suffered from sporidiosis,and displayed dorsolateral humps or swollen abdomen,which lost their ornamental value and caused a small number of deaths.In order to identify the specie of parasite and enrich its epidemiological data,the lesion tissues from dorsolateral humps and hepatopancreas of diseased fish were collected.Morphological observation and spores measurement were carried out.18S rDNA gene of the parasites was then cloned,sequenced and analyzed.The results showed that the morphological characteristics of the spore was pyriform in shape,and two polar capsules arranged in an octagonal shape at the front which accounts for about half of the entire length of the spore.The measured data of the spores were 17.58 μm and 18.09 μm in average length,11.02 μm and 11.82 μm in average width,and there were 7-9 loops of polar filaments,which were similar to those of M.wulii. The partial sequences of 18S rDNA gene of the parasites had the highest homology with M.wulii based on blast from GenBank,and the similarity was more than 99%.In addition,in the constructed phylogenetic tree by 18S DNA gene,the isolated spore was also clustered with the M.wulii.Therefore,it was confirmed that the parasites caused goldfish sporidiosis in these two cases were both M.wulii,and this was the first report that M.wulii parasitized in goldfish muscle.