The aim of the study is to investigate the relationship between university students' level of democratic citizenship behaviors and their social media usage through social capital theory. University students' involvements in democratic issues are both affected by and happens though social media due to the rapid developments in mobile technologies. Thus, it is worthwhile to explore its effect. The study utilized a quantitative approach for both data collection and analysis. The participants of the study were students of Turkish state universities. The total number of the students involved in the study was 2253. The data was gathered by 7 scales developed for the study. One of the scales was yes/no type and the rest were Likert type scales. The data was subjected to stepwise regression analysis. Among all the variables that were in regression models, it appears that 'trust' is the most important single variable in explaining students' different citizenship behaviors.