A group of 82 households in a new-built apartment complex in Seoul, Korea participated in an investigation to examine the symptoms of sick building syndrome (SBS) using of houseplants for two observation periods. The present study confirmed the decrease of formaldehyde content in an airtight chamber containing a pot with fatsia plants. Houseplants affected the general air conditions, such as increasing relative humidity and decreasing carbon monoxide and carbon dioxide. The toxic chemical substances responsible for SBS persisted at least one more years but were effectively decreased by ventilation. Houseplants facilitated the quantitative decrease of some of these chemical substances in indoor air. Indoor-dwellers felt the decrease in SBS symptoms with time regardless of houseplants in both observation periods. Houseplants made a slight difference to the symptom degree of SBS in the first observation period but a significant difference in the second observation period; however, houseplants made little difference to the content of toxic chemical substances in indoor air except formaldehyde, although houseplants gave desirable results in the decrease of SBS symptoms.