Purpose: This study investigated depression and anxiety in girls with precocious puberty and in their mothers. Method: This study recruited 75 girls treated with a gonadotropin-releasing hormone agonist (GnRHa) and their mothers from October 2017 to April 2018. The girls completed the Korean Children’s Depression Inventory (KCDI) and Maturity Fear Scale (MFS), and their mothers were surveyed with the Korean Beck Depression Inventory (K-BDI) and Korean Beck Anxiety Inventory (K-BAI). Results: The K-BDI scores showed statistically significant differences according to girl’s age (p<0.016) and household income (p<0.037). The anxiety scores showed statistically significant differences according to girls’ Body Mass Index (BMI) (p<0.029) and household income (p<0.005). There was a positive correlation between depression in girls and mothers (r=0.264, p<0.050). Conclusion: Our findings suggest a need for understanding and counseling for depression in both girls’ and their mothers during the process of diagnosis and treatment for precocious puberty.