An indoor air purifier has a base and a container on the base with a layer of soil supported above a lower water bath occupying the bottom of the container. The container is fitted on top of the base such that the container can freely rotate upon the base. Room air is drawn into the base and is passed from the base into the bottom of the container through a duct connected between the two. Air passing from the base is directed downwardly into the water bath before passing upwardly into the soil layer. The air passes through the soil layer and is discharged from the soil's surface back into the room. Contaminant gases and particulates are removed from the air through contact with the soil layer and are metabolized by microorganisms contained within the soil, producing carbon dioxide and water. The water bath humidifies the air being passed through it and maintains a stable degree of moisture in the lower portion of the soil layer. Water lost through evaporation is replenished through a sleeve passing downward from the soil's surface to the water bath. A water bottle inverted within the sleeve maintains a substantially constant water level. Plants may be grown in the soil layer to aid in purification and to provide an attractive room decor.