The present invention describes a wastewater treatment method by a microorganism decomposing Tetramethyl Ammonium Hydroxide (TMAH) which, utilized in etching the surface of silicone chip in semiconductor manufacturing process, is toxic and hard to decompose. The present invention provides novel microorganisms capable of decomposing TMAH. Also, the present invention provides a treatment method for wastewater containing TMAH, using the microorganisms. The present invention is useful in industrial field as an environmental friendly wastewater treatment method by decomposing over 90% of TMAH, one of environmental contamination materials in the wastewater of semiconductor factory.