Background: Appointment scheduling is considered as one of the important aspects of patient flow management. Today, the advent of Internet into the realm of health care has paved the way for employing an internet-based booking system for visiting physicians. Therefore, this study aimed at assessing the online outpatient booking system in Iranian hospitals. Methods: The present study was an applied descriptive study. In this study, all outpatient appointment booking websites in Iranian hospitals were evaluated. The methods of outpatients booking in the hospitals (N = 598) were determined based on information available at their active websites. Finally, 31 active online booking systems were identified and investigated using a localized checklist, including 59 items in 6 sections. Results: The results showed that only 13.03% of Iranian hospitals had an active online booking system. All the online booking systems had a weak quality based on the total score percentage (17.10%). The highest score percentages were related to sections of online security features (45%) and details of health insurance (42%), while the clinical data section received the lowest score (7.25%). The most frequent item was the patient’s name in the patient demographics section (27 websites). Conclusions: The outpatient appointment system in Iranian hospitals is done more traditionally through walk-ins to the health centers. The online outpatient booking systems have poor quality. Hence, codification and communication of national standards for designing hospital websites, periodical evaluation of appointment booking websites by ministry of health, and survey of the users of this method can enhance the qualitative level of these websites.