Conversion rate optimization is one of the top priorities for numerous online businesses. Companies want to optimize the number of purchases, email sign ups, registrations or other website performances. Nevertheless, when trying to increase the conversion rate they often neglect the usability aspect of the website. In this thesis, we examine whether improvements in the usability of a website also lead to an increased conversion rate. In order to analyze this issue, we decided to run a series of A/B tests on the job searching portal Profesia.sk. After locating a usability issue, we proposed and developed a solution. Furthermore, we split the traffic in two halves and displayed the improved version of the website only to one half of the users. After reaching a significant sample size, we stopped the experiment and compared the conversion rates of both versions. By using the A/B testing method, we were certain that the differences in conversion rates were caused by modifications that we made and not due to seasonal trends or coincidence. In the majority of our experiments, we considered a conversion to be sending an application to a job offer. The results of the experiments proved that there is a correlation between usability and conversion rate. Although in some experiments there was only a negligible shift in the conversion rate, especially in experiments which handled a serious usability flaw, the improved versions performed significantly better. In this thesis, we showed that enhancing usability leads to a higher conversion rate.