Assisting the chemical plant to improve its wastewater treatment ability was the primary objective of this study. The main products of the chemical plant were textile chemicals and plastic lubricants. Study items included 1. wastewater quality and quantity investigation, 2. treatability experiments, 3. process planning and functional design, 4. construction consulting, 5. start-up assistance and 6. operator training. Three streams of wastewater in the chemical plant are: 1. rich ammonia sulfate wastewater, 2. high COD concentration wastewater and 3. low COD concentration wastewater. Some non-biodegradable or inhibitive compounds were also found in the wastewater. According to experimental results, rich ammonia sulfate wastewater could be restored and produce reusable products by the crystallization process. Moreover, combined low COD wastewater and chemical pretreated high COD wastewater could be treated by PAC-flocculation followed by Sequencing Batch Reactor process. The effluent could meet the 1993 Effluent Standards of Taiwan