Background Dry eye is a common disease worldwide.Cyclosporine A(CsA) is provided to be a immunosuppressive agent and is effective on dry eye.But in China,0.05％ CsA is not yet applied in dry eye treatment.Objective This study was to evaluate the efficacy and safety of 0.05％ CsA eye drops in the treatment of dry eye.Methods This was a randomized,double-blind,vehicle-controlled parallel group study.Forty eyes of 40 patients with moderate to severe dry eye were randomly divided into two groups,with the corresponding treatment of 0.05％ CsA eye drops or the vehicle emulsion.The patients in both the groups received non-preserved artificial tear.Symptoms and signs were observed before administration,(7±1),(28±2),(56±3),and (84±3) days and also 14 days after withdrawal.The clinical effective rate was considered as the primary outcome.The subjective assessment of the patients including total symptom scores and ocular surface disease index (OSDI) scores,Schirmer Ⅰ test (S Ⅰ t) with topical anaesthesia,tear film breakup time (BUT),rose Bengal and fluorescein staining scores were evaluated.The safety profile was evaluated by adverse events,visual acuity and ocular tolerance.Results At the end of this trial,the ocular symptoms scores,conjunctival hyperemia,BUT,S Ⅰ t and keratoconjunctiva staining scores of the two groups had statistically significant difference.The total effective rate of 0.05％ CsA treatment group was 75％ (15/20) and vehicle group was 25％ (5/20).There was a statistically significant difference between groups (P =0.000),and the 95％ confidence interval (C1) of the difference value of total effectiveness between the two groups was 30.80％-53.75％.At the end of this trial,there was no statistically significant difference in visual acuity distribution (P =0.890).No obvious discomfort was found in the patients received 0.05％ CsA eye drops.There were no adverse events during the follow-up duration.Conclusions 0.05％ CsA ophthalmic emulsion is an effective and safe treatment for dry eyes.