Gurami (Osphronemus gouramy Lac.) is a popular fish species among Indonesian people. Several Gurami strains have been cultivated by fish farmer, one of which is Gurami Soang. This strain is belived to have a faster growth rate compared to other strains. However, like other strains, the fingerling of Soang strain have also a low survival and suceptible to disease, especially that caused by Aeromonas hydrophila infection. It has been proved that seeds from a single spawning event show varibale disease resistance. The difference in resistance among individuals is suggested related to the difference in their genetic component. One of the genes responsible for resistance is Major Histocompatibility Complex (MHC) class II B gene. Variability in resistance can be analyzed by using PCR -RFLP technique. PCR-RFLP is a technique that can produce a specific DNA fragments by PCR, followed by cutting the PCR product using restriction enzymes to describe the presence or absence of restriction sites in DNA fragments. This research aims to determine genetic marker to differiantiate between resitant and irresistant individual of Gurami Soang infected by A. hydrophila which die at a different time priod based on PCR-RFLP MHC class IIB gene. The study used survey method with purposive random sampling. This study was done from November 2015 up to April 2016. The Data of PCR-RFLP band patterns were analyzed descriptively. The result indicated that cutting of the MHC class II B gene using HinfI produce two RFLP bands with 300 bp and 100 bp length in all samples. Meanwhile, the MHC IIB gene was not cuted by PstI, HindIII, BamHI and EcoRI enzymes forall samples. These mean that MHC II gene in all individuals were monomorphic. Therefore,it can be concluded that there is no specific genetic marker to differentiate gurami soang individulas which was dying in different time periods. Keywords: Gourami Soang, PCR-RFLP, genetic diversity, MHC class II B gene AbstrakIkan Gurami (Osphronemus gouramy Lac.) merupakan jenis ikan yang populer di masyarakat Indonesia. Gurami soang merupakan strain ikan gurami yang memiliki laju pertumbuhan yang lebih cepat dibanding dengan strain yang lain. Namun, strain soang juga memiliki kelangsungan hidup yang rendah dan rentan terhadap penyakit. Penyakit ikan yang sangat berbahaya adalah yang disebabkan oleh bakteri Aeromonas hydrophila. Benih yang berasal dari satu pemijahan memiliki ketahanan terhadap penyakit yang bervariasi sehingga jika diinfeksi oleh bakteri A. hydrophila akan memiliki ketahanan berbeda-beda. Perbedaan daya hidup tersebut dapat terjadi karena perbedaan komponen genetik yang dimiliki pada setiap individu dalam satu pemijahan. Salah satu gen yang bertanggungjawab terhadap resistensi adalah gen Major Histocompatibility Complex (MHC) kelas II B. Variasi resistensi dapat dianalisa secara molekuler menggunakan teknik PCR (Polymerase Chain Reaction) -RFLP (Restriction Fragment Length Polymorphism). PCR-RFLP merupakan suatu teknik yang dapat memperbanyak fragmen DNA tertentu melalui PCR, d...