Background It is the first multicenter clinical study in China to investigate zanamivir use among Chinese adolescents and adults with influenza-like illness (ILI) since 2009,when inhaled zanamivir (RELENZA(R)) was marketed in China.Methods An uncontrolled open-label,multicentre study to evaluate the antiviral activity,and safety of inhaled zanamivir (as Rotadisk via Diskhaler device); 10 mg administered twice daily for 5 days in subjects ≥12 years old with ILl.Patients were enrolled within 48 hours of onset and followed for eight days.Patients were defined as being influenza-positive if the real-time reverse transcriptase-polymerase chain reaction (rRT-PCR) test had positive results.Results A total of 400 patients ≥12 years old were screened from 11 centers in seven provinces from March 2010 to January 2011.Three hundred and ninety-two patients who took at least one dose of zanamivir were entered into the safety analysis.The mean age was 33.8 years and 50％ were male.Cardiovascular diseases and diabetes were the most common comorbidities.All the reported adverse events,such as rash,nasal ache,muscle ache,nausea,diarrhea,headache,occurred in less than 1％ of subjects.Mild sinus bradycadia or arrhythmia occurred in four subjects (1％).Most of the adverse events were mild and did not require any change of treatment.No severe adverse events (SAE) or fatal cases were reported.Bronchospasm was found in a 38 years old woman whose symptoms disappeared after stopping zanamivir and without additional treatment.All the 61 influenza virus isolates (43 before enrollment,18 during treatment) proved to be sensitive to zanamivir.Conclusions Zanamivir is well tolerated by Chinese adolescents and adults with ILls.There is no evidence for the emergence of drug-resistant isolates during treatment with zanamivir.(ChiCTR-TNRC-10000938)