Background: The aim of this study was to assess the relationship between the number of steps a day and biological (body fat, lean body mass, BMI and estimated VO2 max) and psychological (self-efficacy, enjoyment of PA and self-perception of body image) factors in 16-18-year-old girls. Material/Methods: The study included data from 60 girls, aged 16-18. Voluntary participants were selected from a public high school in Poland. Number of steps was measured with a pedometer Yamax Digi-Walker, model SW 701, during 7 days. Girls were classified into three groups: low active, slightly active and active (5,000-7,499; 7,500-9,999; ≥ 10,000 steps/day, respectively). The levels of psychological factors were determined by means of a questionnaire survey. Estimated VO2 max was assessed by a 1-mile walk test. The percentage of body fat and lean body mass was evaluated using Bodystat 1,500, bio-impedance method. Results: Analysis of variance showed no statistically significant differences in the biological and psychological variables among low active, slightly active and active girls. Conclusions: Girls in the study performed approximately from 5,000 to 12,500 steps a day. To explain better relationships between daily step counts and psychological and biological variables future research should additionally involve girls with less than 5,000 steps a day and more than 12,500 steps a day.