Background Intranasal corticosteroid (INCS) is one of the most effective treatments for allergic rhinitis (AR). To achieve optimum efficiency while avoiding adverse effects (AEs), patients must comply with and follow the drug administration instructions. Objective To evaluate INCS administration techniques and steps and the association between inaccurate drug administration and AEs. Methods A descriptive cross-sectional study was performed in patients diagnosed with AR who had used an INCS for more than 1 month at the HRH Princess Maha Chakri Sirindhorn Medical Center, Nakhon Nayok, Thailand between September 2020 and August 2021. Patient information was collected, evaluate the accuracy of the application techniques and the steps they followed for INCS administration and the occurrence of any associated AEs. Results In total, 150 subjects diagnosed with AR met the criteria. Only 6 patients (4%) correctly performed all 12 steps of INCS administration, while 44 patients (29.33%) correctly performed the 5 recommended essential steps. AEs were found in 23 patients (15.33%), with not pointing the tip slightly outward away from the septum significantly associated with a 3.6 times higher risk of AEs in patients (odds ratio, 3.6; 95% confidence interval, 1.3–9.4; p = 0.012). Conclusion Investigations into INCS use in patients with AR revealed that only 4% of patients correctly performed all the administration techniques and steps, while 30% of patients at least followed the 5 recommended essential steps perfectly. Not pointing the tip slightly outward away from the septum was found to result in the most AEs. Trial Registration Thai Clinical Trials Registry: TCTR-20210718003