Objective To evaluate the application of cough reflex testing with various concentrations of citric acid for dysphagia post stroke. Methods 20 normal controls (NC), 20 stroke patients with dysphagia (SD) and 20 stroke patients without dysphagia (SND) were tested with cough reflex inhalated 4 kinds of dosage of citric acid: 0.2 mol/L, 0.4 mol/L, 0.6 mol/L and 0.8 mol/L. Results The incidence of pass (coughed twice or more) decreased in the SD compared with those in the NC as inhalated citric acid of 0.2 mol/L and 0.4 mol/L (P< 0.05), and decreased under 0.4 mol/L compared with the SND (P<0.05). There was no significant difference between the SND and the NC (P>0.05). 90% of the NC passed as inhalated citric acid of 0.4 mol/L; however, it was 45% in the SD, and increased when they inhalated more dosage of citric acid (P<0.05). The incidence of pass decreased under 0.2 mol/L citric acid in the SND compared with other concentration (P<0.05). The result of the test was reliable interrater (κ=0.97). The incidence of cough was consistent of 96.8% with the same concentration. No asthma and asphyxia was observed. Conclusion Cough reflex testing with citric acid inhalation can be used to assess the defensive function of airway in lower concentration for dysphagia after stroke.