This research focuses on religious subgroup evaluations by examining the attitude of Turkish-Dutch Sunni Muslims towards Alevi and Shiite Muslims. Following the Ingroup Projection Model, it was expected that Sunni participants who practice Islam will project their self-defining subgroup practices on the superordinate Muslim category, which will be related to more ingroup bias towards Alevis, a Muslim subgroup that performs different religious practices. Two studies yielded consistent evidence that practicing Islam increased ingroup bias towards Alevis. Furthermore, in Study 2, we found evidence that the effect of practicing Islam on ingroup bias was mediated by relative ingroup prototypicality (RIP). Moreover, practicing Islam did not affect RIP in relation to Shiites who perform the same religious practices that we examined. These findings support the Ingroup Projection Model.