Fasting during Ramadan is prescribed for every healthy Muslims after the age of puberty whereas the special people such as elderly, sick, children, and etc are among those exempt. However, some patients ask to know whether it is safe to fast if they decide to fast. The aim of this study was to evaluate the influence of Ramadan on kidney recipient volunteers. We conducted a prospective study on 41 adult kidney transplant recipients who chose to fast during Ramadan and 48 recipients who had not fasted at three university transplant centers in the month of Ramadan (September– October 2007). Volunteers were allowed to eat freely from iftar to sahar (dusk to dawn), the average duration of fasting was 14 hours a day. The two groups were matched for age, gender, body mass index (BMI), source of donor (living or cadaver), immunosuppressive regimen, and time since transplantation. All 82 recipients underwent transplantation at least 1 year prior to the study and all had stable renal function for at least 6 months prior to the study with creatinine clearance values higher 60 ml/min. The exclusion criteria were history of acute tubular necrosis due to dehydration; patients who were below 18 years of age; uncontrolled or poorly controlled hypertension or diabetes mellitus; Pregnant patients; concurrent disorders such as chronic liver disease, advanced cardiac disease, acute infection, or diabetes insipidus, active peptic ulcer, or nephrolithisis; no need for medications more than twice a day; and polyuria (urine volume: 2.5 L/d). For each patient, we recorded body weight, BMI, blood pressure, as well as urinalysis, and serum levels of blood urea nitrogen, creatinine, uric acid, blood glucose, electrolytes, lipids, and hemoglobin. All parameters were assessed before, during, and after the month of fasting. The mean ages of the fasting and control groups were 42 ± 12 years and 43 ± 12 years, respectively, and the corresponding times since transplantation were 10-210 (average: 65) months and 11-180 (average: 69) months. Our results showed that GFR did not significantly changes during Ramadan for either group (mean calculated GFR in pre and post Ramadan were 72.8 ± 27.8 and 73.1 ± 29.3 in faster group, P< 0.05; and 73.4 ± 18.8 and 73.1 ± 18.5 in non-fasters, P< 0.05). No statistically significant difference in other parameters was noted between these two groups. The results did not show any adverse effects of fasting, especially on allograft function, in kidney recipients who have stable renal function prior to fasting.