The Formosa Petrochemical Corporation (FPCC) has operated the No. 6 Naphtha Cracking industry site at Mailiao of Yunlin County for 14 years since it completed the construction in 1995. Although the plant were assessed according to the process of environmental impact assessment as required by government¡¦s guidelines before the approval of FPCC establishment at the site, there is a need to re-evaluate the site strictly for problems resulting from the industry activities over the year. The present study is initiated to research and assess the environmental monitoring data collected over the years to determine the spatial and temporal trend of heavy metal contaminants associated with the FPCC operation at site and its coastal areas. The data information used in this study consist of government annual survey reports with regard to the oceanography data of the site, seawater, sediment, and air quality. The FPCC¡¦s monitoring data are also evaluated for including in the environmental quality assessment of Mailiao coastal areas. The present study employed the annual total contaminant discharges reported by the FPCC for obtaining the total burden emitted into the nearby counties Taihsi and Lunbei. The results showed that the coastal marine environment around the industrial site and the Jhuoshuei River have major immediate impacts and problems from the activities. The results of sediment metal content have substantial increase over the years, although the value of metal concentrations is proclaimed that it is within the government provisional guidelines of sediment contaminant standard. In the current circumstance, there are no standard criteria for sediment metal concentration in the marine environment reported elsewhere in the world with exception of Canada. The air quality results showed that Lunbei which is located east side of FPCC site have a decreasing trend of contaminant discharge compared with Taihsi which is located at southern side of FPCC site have a increasing trend of contaminant discharge. Nevertheless, the FPCC site have an increasing total annual discharge. The present study also conducts a survey at Mailiao and Taihsi residences on the social-economic development and the influence associated with the FPCC operation. The survey consists of all stakeholders such as government municipality official, marine aquaculture farmers, non-government organization and fishery cooperation representatives. They are concern the influence on the social-economic development and environment impact from the industry operation. These include the problems of low spat rating in oyster farming and dust falling into the marine farm site to cause the death of bivalves. The health of local residences from FPCC site is of concern due to the expansion program of plan to the site. The present work shows the change and alteration of marine environment resulting from the FPCC activities that have worsened the sustainability development of coastal area.