This study will evaluate the efficacy of as-needed Budesonide/formoterol Turbuhaler 160/4.5 µg/d in the period of step down in well controlled asthmatic patient comparing with standard maintenance therapy in step-2 management in asthma guildeline which is low dose inhaled corticosteroid.

The study will measure the efficacy of as-needed low dose ICS/ LABA in well controlled asthmatic patient comparing with low dose ICS in step down circumstance.

Inclusion Criteria:

1. Patients who have been diagnosed as asthma at least 6 months.
2. Patients who have well controlled asthma by ACT > 23 and ACQ-7 < 0.75 at least 12 weeks with using budesonide/formoterol (160/4.5 μg/d) twice daily
3. Patient who not be taking oral bronchodilator such as montelukast, theophylline, doxophylline but accept for taking anti histamine and intranasal steroid.
4. Patients who able to do spirometry without contraindication.

Exclusion Criteria:

1. History of using systemic steroid previous 12 week and respiratory infection History of pulmonary tuberculosis with residual lung lesion by chest radiograph recent serious medical condition such as myocardial infarction, stroke, pneumonia etc.
2. History smoking less than 10 pack-years or be smoking
3. History of asthma exacabation previous 12 week