The study aimed to find out whether bacteria (Pasteurella multocida) that is isolated from buffalo in HSU (Hulu Sungai Utara) is the cause of SE (Septicema epizootica) disease in the swamp buffaloes using Koch Postulates. Total of 10 Balb-C mice of two weeks-aged were infected with 100 μl cultured containing 4  108 CFU (1.5 McFarland Scale) of P. multocida subcutaneously in the neck, and observed every 4 hours until the animal died. Samples were taken from the spleen, lungs, and heart with different times of death within 15, 35, and 59 h with sterile swab cotton. Samples were cultured on a nutrient broth medium (NB), inoculated on a soy trypticase agar (TSA), and incubated for 24 h at 37 °C. Separate colonies were stained with Gram and spore staining. The colonies were tested by catalase, biochemical, indol motility (SIM) sulfite, confectionary, and planted on Mac Conkey Agar media. P. multocida was identified following Carter's method of showing lung, spleen, and positively infected P. multocida samples. It was concluded that P. multocida bacteria isolated from buffalo in HSU are pathogenic and can cause SE disease. Keywords: Pasteurella multocida, Koch postulates, SE (Septicemia epizootica) and Subcutaneous