Potato virus Y (PVY) is the type member of the genus Potyvirus in family Potyviridae. PVY has a worldwide distribution and is one of the most economically important viruses in tobacco. PVY causes limitation of assimilation, gas exchange, inhibition of water and mineral salts transport to leaf tissues. It affects changes in cell metabolism, resulting in changes in the chemical composition of tobacco, and finally it affects the taste and aroma of cigarettes. The objective of this study was to determine changes in content of nicotine, nornicotine, proteins and reducing carbohydrates in tobacco infected with the PVY. Nicotiana tabacum ‘Xanthi’ plants were grown in a temperature- and humidity-controlled growth-chamber. In the growth-chamber the temperature was 20 °C. Day length was 16h with fluorescent light. Fourteen days after artificial inoculation individual plants were sampled and analysed for alkaloids, proteins and reducing carbohydrates. The control plants were not infected. The artificial inoculation of the plants caused a decrease in average nicotine and nornicotine content by 71% and 9%, respectively. At the same time the conversion of nicotine to nornicotine increased by 47%. The average content of true protein in tobacco leaves 14 days after inoculation decreased to 10.83%, while the sugar content increased by 8% to 15.95% of dry matter. It was found that the virus infection has a significant impact on the chemical composition of tobacco.