Background/aim There are studies on the effects of Ramadan fasting (RF), which is one of the intermittent fasting diets, on both hypertension and endothelial function. However, the relationship between possible improvements in endothelial function and blood pressure after RF is not clear. In this study, we aimed to evaluate the effects of RF on blood pressure and endothelial dysfunction in patients with arterial hypertension (HT). Materials and methods Sixty-four HT patients, aged 45–65, who were followed up in the Cardiology Department of Kayseri City Hospital and fasted during Ramadan between 13 April and 13 May 2021 with their self-consents were enrolled to study. Body mass index (BMI), blood pressure, and flow-mediated dilatation (FMD) were assessed before and after Ramadan. Also, 5 mL venous blood samples were taken between 8:00 and 8:30 a.m. from all participants to assess cortisol, C-reactive protein (CRP), and other laboratory data. Results In patients, FMD values were found to be higher after Ramadan compared to values before the fasting period (p < 0.001). CRP and cortisol levels decreased after fasting, and the decrease in CRP (95% CI for B = −1.685 – −0.334, p = 0.009) and cortisol levels (95% CI for B = −0.392 – 0.092, p = 0.039) were determined as the predictive factors for FMD after RF. Conclusion Endothelial functions as determined by FMD improved after 30 days of intermittent fasting. The decreased CRP and cortisol levels may contribute to the improvement in FMD after RF.