Background Body composition analysis by bioimpedance is a modern investigation method that provides and Study Aim additional and relevant information, compared to the classical assessment, based only on BMI levels. The purpose of the research is to compare body composition parameters for secondary school girls, according to the stages of puberty and to identify the differences that appear between these stages. Material and Methods The investigated group was made up of 115 non-athlete girls from the urban environment, divided into two distinct age categories: 10-12 years/55 cases (Under 12 with age=10.97±0.40, BMI=19.53±3.71, percentiles BMI=65.52± 25.78) and 12-13 years/end of puberty/60 cases (Over 12 with age=12.30±0.30 BMI=20.72±3.62, BMI percentiles=66.13±28.23). The assessment carried out with Inbody 720/Biospace (Korea). Results Reporting to the percentile ranges indicates the absence of Underweight cases for the Over 12 group and only 7.27% of the Under 12 group falls within these values. In both groups, the Normal Weight class dominates (67.27% for Under 12 and 63.34% for Over 12), and the percentages of Overweight and Obese cases are higher for Over 12 (23.33% and 13.33%, respectively). The distribution according to body composition indicates the slim type for about a quarter of the students of both groups, but also the placement of a large number of subjects in the Chubby/normal type category (29.10% for Under 12 and 20% for Over 12). According to the percentage of mass fat, the Over 12 group has a double percentage of Obesity for high level, compared to Under 12 group (23.33% vs. 10.90%). The Over 12 group has statistically higher values (P[removed].