The purpose of this study is to determine to what extent the personality traits based on the Five Factor Theory (extraversion, neuroticism, agreeableness, conscientiousness, openness to experience) predict loneliness levels of university students. The study group of the research was composed of 433 students (260 female and 173 male students) who were attending Inonu University and Nigde University in the academic year of 2013-2014. As the data collection tools, the UCLA Loneliness Scale and the Five Factor Personality Inventory were used in the study. The data analysis was performed using correlation and multiple regression analysis methods. According to the findings of the research, the personality traits of extraversion, neuroticism, agreeableness, and openness to experience are significant predictors of university students' loneliness levels. Consequently, the personality traits based on the Five Factor Theory explained 28% of the variance in loneliness scores of university students.