BACKGROUND: Citrus sinensis juice (CSJ) is a rich source of dietary flavonoids which reduce the risk of adverse cardiovascular events. This study aimed to examine the effects of four-week intake of natural and commercial orange (Citrus sinensis) juice on blood pressure in healthy volunteers. METHODS: In this single-blind randomized crossover study, 22 healthy subjects (age: 18-59 years old) were included and randomly divided into two groups of 11. Group A consumed commercial CSJ during the first four-week period. After a two-week washout period, they consumed natural CSJ for another four weeks. The procedure was reversed in group B. The participants were asked to drink 500 ml/day of either natural or commercial CSJ twice a day with breakfast and dinner. The effects of orange juice on blood pressure were evaluated. RESULTS: After drinking commercial CSJ, diastolic and systolic blood pressure were significantly decreased (5.13%; P = 0.03 and -5.91%; P = 0.003, respectively). However, consumption of natural CSJ did not have significant effects on either diastolic or systolic blood pressure. CONCLUSION: Commercial CSJ significantly decreased blood pressure. Higher flavonoid, pectin, and essential oils content of concentrated products compared to natural juice might have been responsible for this finding. Nevertheless, further studies to focus on dose-response effects are recommended.   Keywords: Citrus Sinensis Juice, Hypertension, Blood Pressure