Inhaled corticosteroid is the foundation therapy in controlling persistent asthma in order to reduce inflammation and prevent deterioration of lung function. There were 75% of asthma patients in RSUD Dr. Soedarso with uncontrolled asthma. Low adherence to inhaled corticosteroid therapy was suspected. This research was conducted to assess relationship between inhaled corticosteroid adherence and severity of airway obstruction through forced expiratory volume1/forced expiratory volume1prediction value and forced expiratory volume1/vital lung capacityprediction ratio. This was an analytic study with cross-sectional design. Data were taken from July 2014 until March 2015. There were 35 subjects who met the criteria. Patient identity, Medication Adherence Report Scale for Asthma score, and spirometry test were obtained directly from the samples. Variables including inhaled corticosteroid adherence, Forced Expiratory Volume (FEV1)/FEVprediction1 value and FEV1/Functional Vital Capacity (FVCpredictio)n ratio were observed. Marginal Homogeneity analysis of the data found significant proportion difference between inhaled corticosteroid adherence and Forced Expiratory Volume1/Forced Expiratory Volumeprediction1 value (p<0.001) and significant proportion difference between inhaled corticosteroid adherence and VEP1/KVP prediction ratio (p<0.001). Low adherence to inhaled corticosteroid therapy causes failure in inflammation suppression and leads to airway remodelling which in turn lead to deterioration of lung function.