Aims: Orthodontic treatment is known as a painful procedure among patients. They feel varying degrees of pain during orthodontic treatment from the stage of initial examination till the end of the treatment. The aims of this study are to explore pain experience among patients undergoing orthodontic treatment with the fixed appliances by comparing two different arch wires sizes. Materials and Methods: The study group consisted of 60 patients (26 males, 34 females) with a mean age of 17.6 years and 20.5 years consequently. Insertion of either 0.014 or 0.016-inch wire was by random selection of patients. Patients were asked to fill out a series of questionnaires for five consecutive days after the insertion of orthodontic initial arch wire, and after the arch wire activation for 4 hours, 6 hours, 24 hours, and till 5 days. The intensity (weak, mild, moderate, severe, and intensive) of the pain symptoms in connection with ten items (Biting on a hard/soft food, sensitive to hot or cold food/drink, mastication of food, fitting anterior and fitting posterior teeth together, cheeks, lips, and tongue pain) have been evaluated. Results: No significant differences were found between age groups, and between the two arch wire groups. Pain perception was more significant in females than in males and the pain perceived at the anterior teeth was greater than posterior teeth. Pain percentage level increased gradually till reaching the peak within 24 hours after the insertion of arch wire and retained the same level in the 2nd day, then decreased till the 5th day. Perceptions of pain by fitting anterior teeth were exactly the same within the period of the first few hours in both arch wire groups, and decreased over the following hours. Conclusion: No age discrimination was found for perception of pain in the two different arch wire groups, with no significant correlation for the time with initial pain that perceived after the insertion of two different initial arch wire sizes then the intensity of pain reduced over the time. Pain was perceived as being greater at the anterior than the posterior teeth and females experienced more pain than males.