Background: The present study was designed to evaluate blood pressure changes in Tehranian 8-13 y old fasting girls during Ramadan and determine effective factors in order to observe blood pressure alteration independently.Materials and methods: Totally, 337 female students aged 8-13 years (mean 10±1 w), ere selected by stratified randomized method among volunteer girls intending to fast the whole month of Ramadan. Study was conducted in three stages; before and during the 2nd and 4th weeks of Ramadan. At each visit, systolic and diastolic blood pressure, pulse rate and pulse pressure, and anthropometric indices were recorded. Girls were also evaluated for pubic hair, breast development and menarche.Results: Totally, 283 girls completed all the three stages. Girls had been fasting for 9±3 and 25±4 days in the 2nd and 3rd visits, respectively. As compared to baseline, there were slight reductions in anthropometric indices during fasting. Mean systolic blood pressure decreased from 102±11 mmHg before fasting to 99±11 mmHg in the 2nd week of fasting and returned to basal level at the end of Ramadan (p<0.001). Mean diastolic blood pressure were 70±9 and 71±8 mmHg before and in the 2nd week of fasting and increased to 74±9 mmHg at the end of Ramadan (p<0.001). Systolic and diastolic pressures were significantly correlated with most anthropometric and pubertal indices. Weight showed the strongest correlation with systolic (r=0.48) and diastolic (r=0.40) blood pressure (p<0.001). Linear regression analysis demonstrated weight as the best predictor for systolic and diastolic blood pressure. Adjusting systolic and diastolic blood pressure according to the weight of the girls did not cause considerable change in their values and patterns during fasting.Conclusion: Blood pressure changes in Tehranian 8-13 year old girls during Ramadan fasting in autumn season were slight, within normal range and independent from weight changes.