The subject of the paper is the role of electronic word of mouth in the decision-making process for purchasing mobile devices over the Internet. The Internet and the digitalization of the world have provided consumers with many options through which they can share their opinions and reviews about a particular product or service. Except for the usual oral presentation, which they are used to, now they are also enabled to do electronic word of mouth. The popularization of social networks, forums and blogs increases the interest in electronic word of mouth as a key factor in the purchase decision process. Today, any person can share their opinion on the Internet either publicly or anonymously. This greatly affects the credibility and credibility of electronic word of mouth. Consumers must assess the credibility and other factors themselves and make their purchase decision accordingly. Online reviews help the consumer gather all the most important information about mobile devices (and other products) so that they can make the most optimal decision before buying. The goals of this thesis were to define and explain electronic word of mouth, the stages of the decision-making process in online purchases, and to examine the role of electronic word of mouth when purchasing mobile devices online. For the purpose of the thesis, primary research was conducted in the form of an anonymous questionnaire. The main factors studied within the thesis: credibility, style of expression, expertise and reliability of reviewers, homophily, quality of information within online reviews, adoption of electronic word of mouth and involvement in electronic word of mouth The results showed that the credibility, style of expression, expertise and reliability of the reviewer, homophily, quality of information within the online review, adoption of electronic word of mouth and involvement in electronic word of mouth have significant role in the process of purchasing a mobile device online.