OBJECTIVE: Thymoquinone (TQ) is an active and potent compound in the oil of nigella sativa, which has anti-inflammatory properties. The aim of this study was to evaluate the effects of TQ on ovalbumin (OVA)-induced allergic conjunctivitis (AC) in Balb/c. METHODS: The mice were divided into seven experimental groups; PBS Con, OVA Con, Conj, 0.05%TQ, 0.1%TQ, 0.5%TQ and Dex group. The mice were immunized and exposed to OVA, and eyes were treated with TQ and dexamethasone. Ocular symptoms were observed after last exposure to OVA. Eosinophils count in blood and Ophthalmic lavage fluid (OLF), recruitment of inflammatory cells in conjunctiva, serum IgE and OVA-specific IgE were evaluated by Giemsa and HE staining, and Enzyme-Linked Immunosorbent Assay (ELISA) respectively. High Performance Liquid Chromatography (HPLC) was used to determine the histamine level in OLF. The mRNA expression and protein level of cytokines were examined by real time RT-PCR and ELISA respectively. RESULTS: Ocular symptoms of AC and other characteristics of allergic inflammation including IgE and OVA-specific immunoglobulin E (IgE) level, recruitment of eosinophils, histamine level, mRNA expressions and protein level of cytokines were remarkably increased in OVA-exposed mice compared with the control groups. Administration of TQ suppressed the ocular symptoms, inflammatory cell infiltration in conjunctiva, blood and OLF, increased level of serum IgE and OVA-specific IgE, and OLF histamine level in OVA-exposed mice. Furthermore, TQ abrogated the mRNA expression and serum level of interleukin including 1L-4, IL-5, IL-13 and transforming growth factor beta (TGF-?) in mice immunized and exposed to OVA. CONCLUSION: Administration of TQ significantly reduced the ocular symptoms in AC by attenuating the recruitment of eosinophils, level of IgE, histamine and cytokines. Our findings suggest that TQ might be a useful intimation for the treatment and future research for AC.