To assess the significance of intraluminal ultrasound in the diagnosis of developmental status and treatment effect in normal and idiopathic precocious puberty (ICPP) girls. Endorectal ultrasonography was used to measure the parameters of uterine length, width, thickness, cervix length, ovarian volume and maximum follicular length in normal girls and compare their differences between pre- and post-treatment by gonadotropin-releasing hormone analogues (GnRHa) in idiopathic precocious puberty girls. The ultrasonic parameters of uterus and ovary in normal girls significantly increased in average 9-year-old girls (1.87 ± 0.58) ml of uterine volume in 9-year-old group vs (1.03 ± 0.24) ml in 7-year-old group; ovarian volume (3.01 ± 2.73) ml of uterine volume in 9-year-old group vs 0.98 ± 0.36 ml in 7-year-old group. They were much greater in ICPP girls and decreased significantly at post-treatment, (1.16 ± 0.19) ml of uterus volume pre-treatment vs (1.02 ± 0.15) ml post-treatment; (2.11 ± 0.48) ml of ovarian volume pre-treatment, (1.72 ± 0.55) ml post-treatment; (1.36 ± 0.25) cm of the biggest follicular diameter pre-treatment, (1.16 ± 0.36) cm post-treatment. Endosonography is an important tool of evaluating the development status and treatment effect in normal and ICPP girls.