This masters thesis covers the topic „Influence of microstructure on the corrosion resistance of steel“. The first part of the thesis consists of a description of the corrosion process along with its internal and external factors and the economical aspects of corrosion. Considering the machanism of formation, classification of corrosion is given along with chemical and electrochemical corrosion characteristics. Basic and special forms of corrosion are observed and most commonly used anticorrosion protection methods are suggested. This thesis defines methodology and application of electrochemical testing of corrosion rate. The last part of theoretical part consists defined and categorized heat treatment processes. In the experimental part, characteristics of low-carbon steel C15E are defined and carburizing heat treatment process is described and performed. Electrochemical testing of corrosion rate was performed in 3,5% NaCl solution for steel specimens before and after heat treating. The entire experimental process is described along with the used equipment. Experiment results are shown using curves of the stationary potential of an open circuit and Tafel plots. From generated diagrams, it is determined that the corrosion rate of specimen in normalised condition is greater than corrosion rate of carburized specimen. Reason for this results is transformated microstructure that doesn't allow formation of microgalvanic cells in electrolite. This masters thesis ascertained that carburizing heat treatment has created martensite microstructure of specimen with greater corrosion resistance than ferrite-perlite microstructure of specimen in normalised condition.