For the last three years Greece holds a dominant place among European countries on youth’s obesity. Poor diet behaviour and physical inactivity are considered the key-factors for this epidemic expansion. The main purpose of this study was to examine physical activity (PA) level in overweight and non-overweight adolescent girls. Additional aims were to a) quantitatively describe the duration and intensity of PA on two weekdays and one weekend, and b) to compare PA level with the international guidelines of PA for health (Cavill, Biddle & Sallis, 2001). Forty two healthy adolescent girls living in two urban areas of Greece, aged 14 yrs (SD ±.8) participated voluntarily at the study; 22 were non-overweight (BMI 21.1, SD±1,2) and 20 were overweight or obese (BMI 27.5, SD±2,7). Their daily PA measured objectively by using the CSA 7164 accelerometer over a 4-day period (two weekdays and one weekend). For each day summary scores were calculated for: a) daily total PA, b) daily moderate PA (MPA) and c) daily vigorous PA (VPA). Compared to their non-overweight peers, overweight girls exhibited significantly lower daily accumulations of MPA and VPA for the weekdays and the weekend. A percentage of 76% of the non-overweight girls fulfilled the recommendation of the 60’min accumulated daily MVPA compared to 21% of their overweight peers. None of the participants accumulated substantial amount of VPA. These findings suggest that physical inactivity is one of the most important contributing factors to the increase of young girls’ obesity in Greece. Efforts should be made to shift the sedentary-light activity to moderate, and to increase the time of involvement on PA over weekend days, especially for the overweight girls.