The purpose of this thesis is to determine how viral marketing effects consumers and their purchasing decisions. The research focus is on specific industry, specifically a product category – cosmetic products. Viral marketing is difficulat to define, but it is essential to emphasize that it facilitates the rapid spread od marketing message. Thus, viral marketing allows the dissemination of marketing message among consumers through various media channels. In this process, consumers are both receivers and transmitters of these messages. In the introductory sections of the thesis, the fundamental concepts of marketing communication are examined with a comparison between traditional and modern forms. Through a detailed analysis of digital and viral marketing, the most important aspects, such as online advertising, its advantages, and the elements influencing the success of viral marketing, are explained. Consumer behavior, as the central unit of this research, is analysed through factors influencing consumer behavior, with a particular emphasis on online consumer bahavior. To explore the topic of this thesis, empirical research, including surveys and focus groups, was conducted. It was proven that viral marketing has a greater impact on females and that entertaining messages that evoke emotions have a greater effect on consumers. Additionally, it has been proven that consumers are inclined to purchase viral products and that they will buy them even if they have no need for them. The focus group additionally confirmed the influence of viral marketing on women, especially when it comes to Korean cosmetics. The implications of this research are manifold, providing useful insights for marketing professionals in creating creative and emotionally engaging campaigns, with a focus on male consumers as well.