This study examined distinctive assumed similarity in Honesty-Humility and Openness to Experience and its influencing factors. With samples from the British Isles, China, and Denmark and with both individual and dyadic data (N = 1196), the meta-analytical results show that distinctive assumed similarity in Honesty-Humility and Openness to Experience was higher than in Emotionality, Extraversion, Agreeableness, and Conscientiousness in intimates after controlling for normativity. Also, relationship satisfaction and commitment moderated distinctive assumed similarity in Honesty-Humility and Openness to Experience, indicating that people high in relationship satisfaction and commitment perceived their partner to be more similar to them regarding those two traits relative to people low in relationships satisfaction and commitment. Implications and limitations of this research are also discussed.