Tolerance between ethnic groups is regarded as an essential ingredient of consolidated democracies. The lack of tolerance is likely to cause small- or large-scale violence, leading to both civil war and the breakdown of democracies. That is why it is essential to capture to what extent ethnic groups have tolerance toward one another and what factors account for (in)tolerance. In this study, by using original and comprehensive data derived from a major public opinion survey, conducted in 2013 with a nationwide, representative sample of 7103 participants, we investigate inter-ethnic tolerance among Turks and Kurds in Turkey, a developing democracy in the Muslim world, challenged by increasingly assertive Kurdish ethnonationalism. The Turkish state has been fighting against the PKK (The Kurdistan Workers’ Party, Partiya Karkaren Kurdistan) since the early 1980s and the fighting between Turkish security forces and the PKK has already claimed around 35000 lives. Despite this bloody conflict between the state and outlawed PKK, we do not see mass-scale inter-ethnic violence between Turkish majority and Kurdish minority. Nevertheless, the growing number of incidences of episodic violence in urban areas and increasing anti-Kurdish attitudes and discourses in society lead us to question the level of tolerance between Turks and Kurds. Our preliminary statistical analyses confirm our doubts and suggest that compared to Kurds, ethnic tolerance remains much lower among Turks. In this research we focus on the possible impact of religion-related factors (e.g. religiosity and sectarian differences) on inter-ethnic tolerance and raise the following questions: Why ethnic tolerance among Turks is lower? What factors do account for the variance in Turkish (in)tolerance towards Kurds and for the Kurdish in(tolerance) towards Turks? Are religious individuals more tolerant? Do sectarian differences (Alevi vs. Sunni division among Turks; Shafi vs Hanefi division among Kurds) matter in tolerance towards another ethnic group? What would the implications be for broader theoretical debate on ethnic conflict resolution prospects and democratization processes?