The adult height of children with early onset puberty is limited by the premature maturation of hypothalamic-pituitary-gonadal axis. To evaluate the effects of gonadotropin-releasing hormone analog (GnRHa) treatment on the final height (FH) and bone maturation rate (BMR) in girls with early puberty (EP) or idiopathic central precocious puberty (ICPP), we examined data from girls who were diagnosed with EP or ICPP and underwent GnRHa (Leuplin Depot: 3.75 mg/month) at China Medical University Hospital, in Taiwan, between 2006 and 2015. Patients were observed until the achievement of FH and divided into an "EP group" (T-ep) and "ICPP group" (T-icpp) according to the age of onset of puberty. Eighty-seven patients were enrolled (T-ep, N = 44, puberty onset at 8-10 years; T-icpp, N = 43, puberty onset before 8 years). The demographic data of girls with EP or IPP was characterized. BMR, change in predicted final height (PFH) after GnRHa treatment, target height (TH) and FH were measured. After GnRHa treatment, the study groups (T-ep: 160.24±6.18 cm, T-icpp: 158.99±5.92 cm) both had higher PFH than at initiation (T-ep: 159.83±7.19 cm, T-icpp: 158.58±5.93 cm). There was deceleration of BMR in both groups (T-ep: 0.57±0.39; T-icpp: 0.97±0.97) and a significant difference between the groups (p = 0.027). The gap in FH standard deviation scores (SDS) and TH SDS had a significant difference in T-ep (p = 0.045) but not in T-icpp. Moreover, there was no difference in the gap of PFH SDS between the 1st and final treatment in both groups. We concluded that GnRHa decelerated BMR in girls with earlier puberty. Further prospective clinical studies are warranted.