The ninth month of the lunar calendar is known as Ramadan, and it is during this time that Muslims make substantial modifications to their daily routines, including their eating, sleeping, and exercise habits. Very little research has been done on the effects of Ramadan fasting on people with Type 1 Diabetes Mellitus (T 1 DM), particularly adolescents. Objectives: The purpose of this research was to determine whether or not fasting throughout Ramadan had any influence on the HBA1c, total cholesterol (TC), triglyceride (TG), low-density lipoprotein-cholesterol (LDL-c) and quality of life (QOL) of a group of Egyptian adolescents with T1DM. Methods: This prospective cohort research was performed at Endocrinology outpatient clinic of (Internal medicine and pediatric department) El-Sayed Galal University Hospital, Cairo, Egypt, before and after Ramadan of Islamic year 1443 Hijri, (April / May 2022). The study was conducted on convenient sample of (T 1 DM) Egyptian adolescent’s patients who accepted to share in research. Baseline characteristics and HbA1c levels, TC, TG, and LDL-c were collected from all willing participants in the 4 weeks preceding Ramadan, an Arabic version of the WHOQOL-BREF questionnaire was administered. All laboratory investigations and Psychometry were repeated within 1 to 2 weeks after Eid-ul-Fitr. Results: Forty-nine (T1DM) patients age ranged from 10 to 18 years were included. HbA1c level of the patients before Ramadan, was 8.29 ± 1.14 % that changed to 7.91 + 1.11% after the Ramadan which indicates significant decrease of HbA1c when contrasting the time following Ramadan to the time before. TC mean levels prior to and following Ramadan were 198.45±47.10 and 185.73±51.99 mg/dl respectively. The mean levels of TG before and after Ramadan were 206.08± 53.41 and 185.43±50.46 mg/dl respectively. The mean levels of LDL-c before & after Ramadan were 92.86±17.17 and 84.33±19.19 mg/dl respectively. There was significant decline in lipid profile after Ramadan compared to their levels before Ramadan. Patients’ self-reported (QoL) mean score before Ramadan fasting was 72.55± 10.84, and their mean score after Ramadan fasting was 93.06± 8.47. Total score of QoL showed significant increase after Ramadan than before Ramadan. Conclusions: Ramadan fasting may have positive impact on HbA1c, (TC), (TG) level and (LDLc) in (T1DM) Egyptian adolescent patients. It may be also associated with improved QOL in (T1DM) Egyptian adolescent patients. Recommendations: Respecting the psychological need for participating in Ramadan fasting on (T1DM) adolescents. Further large multi-center study is needed to explore effects other related variables on QOL among (T1DM) adolescent patients.