The aim of this work was to determine the approximate value of the molecular mass of an exogenous biomolecule synthesized by the Bacillus vallismortis AZ-130 strain isolated from oilcontaminated soils of Azerbaijan and to determine the degree of its stability at low pH values. To achieve the goals, strain AZ-130 was cultivated for 24 hours on a shaker with constant shaking (180 rpm) at 32°C. Next, a supernatant was obtained from the culture solution, which, after the addition of trifluoroacetic acid and 10-fold concentration using 3K MWCO Amicon Ultra-15 Centrifugal Filter Devices centrifugal filter concentrators, was examined by the growth inhibition assay for the presence of activity against S. aureus ATCC 29213. Based on the obtained results, it was found that the bioactive molecule produced by the AZ-130 strain is stable at low pH values and has a molecular mass of more than 3000 Daltons.