Family harmony is likely to be challenged if children perceive that their parents do not treat them and their siblings fairly. The direction of parental favor is related to an individual’s perception of fairness but does not fully explain it. The current study investigated whether personality traits moderated the relationship between parental differential treatment and fairness perception. A total of 762 undergraduates (aged between 18 and 25) completed the Big Five Inventory and nominated a ‘target sibling’ whom they considered as they completed the Sibling Inventory of Differential Experience and rated the fairness of parenting. Regression analyses showed that slightly more affection towards the participant and slightly more control over the target sibling were evaluated as most fair, whereas extremely unequal parental treatment (regardless of who was favored) was evaluated as very unfair. Of the Big Five personality traits, agreeableness, extraversion, and openness moderated the fairness perception of parental differential affection but not parental differential control. Favored individuals who were highly agreeable and open to novelty were less likely to rate affection preference as fair than favored individuals who were of low agreeableness and low openness. Also, individuals high on extraversion rated both extreme parental favor and disfavor as less fair than individuals who were low on extraversion. The current study highlights the importance of personality in the fairness perception of parental differential treatment. Implications for parents and family practitioners are provided.