From the beginning of being a pioneer in the production of hot-rolled structural steel in order to support the expansion of the construction industry and substitute imports, giving SYS an opportunity to stabilize the country's economy. For over a decade SYS has grown and developed into the country's largest hot-rolled structural steel producer and is determined to move forward to become a hot rolled structural steel producer in ASEAN.

Siam Yamato Steel Company Limited or SYS (S-Y-S) was established in 1992 with the objective of establishing to produce hot rolled structural steel which is a joint venture between Yamato Kogyo Co., Ltd., Mitsui & Co., Ltd., Thai Cement Public Company Limited, Sumitomo Corporation (Thailand) Co., Ltd. and Mitsui & Co. (Thailand) Co., Ltd..

Currently, SYS has 2 factories located at Map Ta Phut Industrial Estate. And WHA Eastern Industrial Estate (Map Ta Phut), Rayong Province, with the production capacity of hot-rolled structural steel up to 1,100,000 tons per year by using modern machinery and production technology in order to produce quality hot-rolled structural steel.