Among many methacrylic monomers, methyl methacrylate (MMA) is the most important. World consumption of methyl methacrylate was about 2.5 million metric tons in 2005 (1). It was predicted that world consumption of methacrylate would grow at a rate if 5.1% each year from 2006 to 2010 (1). Application of MMA is mainly in construction/remodeling activity, automotive applications and original equipment manufacture. In 1933, first commercial production of MMA monomer started in Germany using original acetone cyanohydrin route (2). In 1934 a patent was issued for the conversion of acetone cyanohydrin to methacrylamide sulfate using concentrated sulfuric acid (3). The methacrylamide sulfate could then be hydrolyzed to methacrylic acid and esterified to form MMA. The methacrylamide sulfate route has dominated the commercial production of MMA since then. In this study, design-based approach methodology (4), (5) is used to obtain life cycle inventory data of MMA manufacturing process. The functional unit is defined as per metric ton MMA production. The methacrylamide sulfate route is designed based on chemical engineering design techniques. Energy requirement of the process is obtained based on chemical engineering unit operation principles and models. Mass balance and energy balance are conducted for each process unit and the overall process. Air, water, and solid emissions from the process are classified and listed in the life cycle inventory result.