The application of composites has a wide range, like structural and decorative elements of the automotive, aerospace and shipbuilding industries, applications in medicine, electrical engineering, and consumer products. However, the wide range of application of composites materials has become a significant problem due to the negative impact on the environment. Most composites today are derived from fossil sources and are not biodegradable, and the increased use of composites and human negligence has led to an increase and accumulation of plastic waste. This created the need for the use of composites obtained from green sources, research into their properties in various environments and the possibility of greater degradability of products after use. Sea water is a specific environment for the use of biocomposites which, due to their numerous influencing factors, affects the properties of biocomposites. In this bachelor thesis, the goal is to investigate the influence of seawater on the mechanical, physical, and chemical properties of selected biocomposites. In the theoretical part, an insight into the advantages and disadvantages of biocomposite materials in relation to synthetically obtained composites, their application and insight into the problems of the marine environment is presented. The experimental part describes the fabrication of selected biocomposites, mechanical, chemical, and physical properties due to the influence of sea water and finally gives a comparison of the results concerning properties of biocomposites tested in normal atmospheric conditions. The last part of experimental work includes hygroscopicity testing and the long-term impact of seawater on the immersed composite. Composites reinforced with flax and jute fibers with a bioepoxy resin matrix of a high content of biodegradable content were selected. Conclusion of this bachelor thesis shows a review of the obtained results and describes the need for future research of biocomposites.