Background:Allergic conjunctivitis (AC) is a multifactorial and common type of ocular surface disease that affects many people. The quality of life for AC patients can be significantly decreased caused by symptoms of ocular itching, swelling, redness, and tearing. Topical antihistaminics, mast cell stabilizers, non-steroidal anti-inflammatory drugs (NSAIDs), and steroids have been widely used to treat AC. Many clinical trials have indicated that olopatadine hydrochloride eye drops can provide quick relief of symptoms and signs. The purpose of this review is to evaluate systematically the effectiveness of olopatadine hydrochloride eye drops for treating AC.Methods:A systematic review of all of the randomized controlled trials on the effectiveness and safety of olopatadine hydrochloride eye drops for AC will be conducted. We will search PubMed, Web of Science (WOS), EMBASE (OVID), the Cochrane Library, Google Scholar, China National Knowledge Infrastructure (CNKI), China Science and Technology Journal database (VIP), Wanfang Database, and CBM, from the database inception date to October 31, 2019. There are no language or publication status restrictions. Registers of clinical trials, potential gray literature, reference lists of studies, and conference abstracts will also be searched. Two reviewers will independently read the articles, extract the data information, and assess the quality of the studies. Data will be synthesized by a heterogeneity test. The primary outcomes include the main symptom and sign scores before and after treatment, the eye redness index, the presence of eosinophils in the conjunctival scraping. Quality of life, the total treatment efficacy, and safety will be evaluated as the secondary outcomes. RevMan V.5.3 software will be used for the meta-analysis.Results:The study will provide an objective and normative systematic review to evaluate the effectiveness and safety of olopatadine hydrochloride eye drops for the treatment of AC.Conclusion:Our review will provide useful information to judge whether olopatadine hydrochloride eye drops is an effective intervention for patients with AC.Ethics and dissemination:It is not necessary to obtain ethical approval as participants are not involved patients. The protocol and results will be published in a peer-reviewed journal. The systematic review will also be disseminated electronically and in print to help guide health care practice and policy.Prospero registration number:PROSPERO CRD42019132232.