Today life without plastic products is unimaginable because of its broad use and relatively easy manufacturing. The most common types of plastic are polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC) and polyethylene terephthalate (PET). A result of its widespread use is the accumulation of plastic waste in the environment, which is not only a threat to the environment itself, but also the health of people and animals that live there. Because of that, new ways of removing plastic waste from the environment in an acceptable way are being researched, and one such method is biodegradation. Biodegradation occurs when microorganisms use their digestive enzymes to degrade the polymer chain of the plastic material. In this thesis the biodegradation of PVC microplastic (MP) using a gram-positive bacteria Bacillus subtilis was investigated. The goal was to determine the optimal conditions of the biodegradation of PVC MP. The experiment design was the Full factorial design with 3 factors on 3 levels: pH (6, 7 and 8), speed of the rotary shaker (100, 150 and 200 rpm) and the optical density (OD) of the suspension (0.1, 0.3 and 0.5). The experiment lasted 30 days during which the number of colony forming units (CFU), concentration of total carbon (TC), organic carbon (TOC) and inorganic carbon (TIC) were determined. After 30 days solid MPs were separated from the liquid phase using membrane filtration. After that the PVC MP was analysed using FTIR-ATR spectroscopy, while LC-MS was used to determine if any additives were released from the PVC MP into the liquid phase. Finally, the toxicity of the liquid phase was determined using the marine bacteria Vibrio fischeri, to determine if any harmful products of biodegradation of PVC were present. The results were analysed using the program Design Expert with the analysis of variance (ANOVA). The optimal conditions for the biodegradation of PVC MP using Bacillus subtilis were: pH = 7,74, speed rotary shaker = 200 rpm and OD = 0,5.