Small Airway Function of Fluticasone/Formoterol (Flutiform®) and Fluticasone/Salmeterol

Inclusion Criteria: 1. Adult (over 19 years) asthma patients 2. Patients who have a history of mild-to-moderate-severe, persistent asthma for at least 6 months prior to Screening. 3. Patients who were required to demonstrate a FEV1 of ≥ 40 % and ≤ 85% of predicted normal values during screening period following appropriate withholding of asthma medications (if applicable). 4. Patients who were required to show reversibility of ≥15% FEV1 after salbutamol inhalation (2 actuations, 100µg per actuation) from the pre- salbutamol value at screening 5. Patients who have uncontrolled asthma by Seretide® 250/50 defined as ACT less than 20 6. Patients who showed R5-20 more than 0.1 kPa/L/s 7. Blood eosinophil count \> 300/µL on screening visit 8. Female patients of childbearing potential must have a negative urine pregnancy test at Screening. 9. Patients who are able to use the inhaler 10. Patients who is willing to voluntarily sign the study consent form Exclusion Criteria: 1. Patients who have experienced life-threatening asthma within 12 months prior to screening or respiratory infection within 4 weeks prior to screening, or patients who have experienced any emergency visit or hospitalization due to acute asthma symptoms within 4 weeks prior to screening 2. Patients who have diagnosed as clinically significant disease or non- reversible pulmonary disease or patients who currently have active pulmonary disease (eg. COPD, cystic fibrosis, bronchiectasis, active tuberculosis) 3. Patients who have diagnosed as laryngitis, chronic sinusitis, infectious rhinitis or allergic rhinitis within 4 weeks prior to screening, or patients who have had any symptoms of acute exacerbation or purulent discharge by the disease above within 2 weeks prior to screening 4. Current smoker or past smoker defined as below: * Current smoker: smoking history within 12 months prior to screening * Past smoker: smoking amount ≥10 pack year\* * Pack year (PY) calculation: average amount of smoking per day (pack) x duration of smoking (year) 5. Patients who currently are pregnant or lactating 6. Patient who had taken systemic corticosteroid within 4 weeks prior to screening 7. Patients who had taken omalizumab within 24 weeks prior to screening 8. Patients who had taken the following medications within 1 week prior to screening: * potent CYP3A inhibitors * β-blockers * monoamine oxidase inhibitor * TCA (tricyclic antidepressants) * quinidine-type anti arrhythmic * Leukotriene anatagonist * Astemizole 9. Patients who are participating or going to participate in any interventional clinical trials 10. QT interval prolongation in ECG result at screening 11. Patients with hypersensitive to investigational products or to any component of the drug 12. Patients who are judged difficult to participate in this investigation by the investigator