Chitosan is a natural polymer which, due to its chemical and biological characteristics, has a role in almost all areas of human activity, from medicine and pharmacy to environment protection. It is a water-soluble copolymer, composed of two types of repetitive monomeric units: N-acetyl-2-amino-2-deoxy-D-glucopyranose and 2-amino-2-deoxy-D-glucopyranose. It can be produced by N-deacetylation of the chitin using chemical processes, and it can be found in nature with certain types of fungi. Furthermore, chitosan is characterized by a low level of toxicity and prominent level of biocompatibility and biodegradability. Due to these properties, chitosan has found its role in environment protection; it is a very useful chelating agent for heavy metals in wastewaters and particulate matter (PM). Chitosan can be produced from the exoskeleton of the arthropod; first, the chitin is isolated, and then in the process of deacetylation is performed to obtain chitosan. It can be then used as a starting material in chemical synthesis of certain products used in medicine, pharmaceutical industry of drugs and environment protection. The molecular weight and its distribution affect physical and chemical properties of polysaccharides such as the rheological, mechanical properties and pore size of membranes or microcapsules made of chitosan. Therefore, molecular weight determination is very important for elucidating the characteristics of the chitosan itself and the products made from it. Gel forming, osmotic pressure modification, viscosity enhancing, or fiber formation also depend on molecular weight and its distribution which have been used in food industrial, pharmaceutical, and medical applications. In this bachelor thesis it is investigated how does reaction temperature and duration time of deacetylation reaction under the mild conditions effect the degree of deacetylation (DD) and molecular weight of deacetylated chitosan. To determine molecular weight of deacetylated chitosan, static light scattering (SLS) method is used by Malvern Zetasizer Nano S instrument while the degree of deacetylation was determined by infrared spectroscopy (FT-IR). By increasing the reaction temperature and time of deacetylation reaction, the degree of deacetylation (DD) have increased. Furthermore, by increasing reaction temperature and time duration of deacetylation reaction, decrease of molecular weight or hydrolysis of polymer chain is also noticed. By the results obtained in this thesis we can prepare chitosan with desired molecular weight and degree of deacetylation what makes chitosan more exploitable and applicable in variety of scientific and industrial fields.