This article investigates the national identity and its relationship with ethnicity and social capital among Iranian university students. The findings show that in Iran, despite ethnic diversity, the observed mean index of national identity is higher than the expected mean. The Persian and Lor ethnic groups obtained the highest, and the Kurdish, and Turkish ethnic groups the lowest mean scores on national identity and social capital. Students majoring in agriculture and humanities obtained the highest, and engineering students the lowest mean score of national identity. Students majoring in science obtained the highest, and engineering students the lowest mean score of social capital. The findings suggest a positive correlation between national identity and social capital. In terms of national identity, there are statistically significant differences among students, but not according to their gender and educational major. In Iran, as a multi-ethnic society, social capital and national identity are directly related. This means that civic national identity and inter-group social capital among Iranian ethnic groups reinforce each other.