This study was carried out to assess the improvement of treatment by the house-plant. For the purpose of this study, 17 asthma-patients residing in Seoul were selected as participants during January to March 2007. We measured VOCs and conducted clinical survey during April to September 2007. In this study, 6 species of houseplants known to be eco-friendly were investigated for the health effect along with 12 other plants. The research focused on peak expiratory flow rate(PEFR) and disease specific quality of life. When the results were compared to the non-intervention households, the intervention households had reduced levels of acetaldehyde, benzene, ethylbenzene, xylene and styrene. The reduction rate estimated from this comparative study was statistically significant(p<0.05). There was however no association between the intervention and the estimated PEFR between morning and evening data in asthma-patients. Keywords : Houseplants, VOCs, Asthma symptom