Abstract. Hikmawati F, Susilowati A, Setyaningsih R. 2018. Detection of the number and pathogenicity of Vibrio spp. on green mussels (Perna viridis) in the tourist area of Yogyakarta. Pros Sem Nas Masy Biodiv Indon 5: 334-339. Yogyakarta Beach is one of Indonesia's tourist areas that attracts local and foreign tourists for its beauty of the beach and delicacy of seafood dishes. Green mussels are the result of marine fisheries that are favored by tourists due to not only the delicious taste of shellfish but also high amount of protein needed by consumers. In 100-gram meat of green mussel contains 21.9% protein which is comparable to chicken eggs. Green mussels have filter feeder properties which cause microorganisms including pathogenic bacteria accumulated at relatively high levels. Bacteria spread through seafood will cause foodborne diseases caused by Vibrio spp. including V. cholerae, V. parahaemolyicus, and V. vulnificus. In Indonesia during 2013, there were 48 food poisoning events consisting of 1.690 sick people and 12 others died. The purpose of this study was to determine the number of Vibrio spp. bacteria based on the TPC (Total Plate Count) test adjusted to Indonesia National Agency of Drug and Food Control (NADFC) standards Number HK.00.06.1.52.4011 in 2009 and to know the pathogenicity of Vibrio spp. with BAP (Blood Agar Plate) media to detect bacterial hemolysis ability. This study uses an experimental method conducted in May 2018 at 3 sampling points that have different conditions (fresh, not fresh, and boiled) in the beach area tourism of Yogyakarta. Vibrio spp. can be grown on the selective agar medium TCBS (Thiosulfate Citrate Bile Sucrose). The results show that 3 green musselslocated in 3 beaches are detected with Vibrio spp.The lowest Vibrio spp. are L3K3 (Kwaru boiled) with a number of 0.002 x 105 CFU / gr while the highest number of Vibrio spp. is the L1K2 sample (Depok is not fresh) which is 0.686 x 105 CFU/gr. From total bacteria, 23 different coloniesare obtained based on colony morphology (shape, elevation, edge, color). Pathogenicity test is obtained by 5 out of 23 colonies which show the results of β-hemolysis. namely L1K2, L1K3, L2K1, L2K2, L3K2.