Siamraj Public Company Limited (formerly known as Siam Rajathanee Corporation Co., Ltd. and Engineering Products Co., Ltd.) was established on February 20, 1984 as Engineering Products Co., Ltd. with a registered capital of 1,000,000 baht initially aimed to design and provide engineered pumps and systems, as well as engineering services for the general industries.

In 2004, the company had expanded into other two businesses which are Metering and Pipeline Transmission and Natural Gas for Vehicles Businesses.

On February 4, 2008, the Engineering Products Co., Ltd had renamed to Siamrajathanee Corporation Co., Ltd., and later on February 2, 2015, the company has transformed to the public company and changed the name to Siamraj Public Company Limited with a registered capital of 300 million baht.

On October, 2017, the Capital increased of Siamraj Public Company Limited from 300 million baht to be

338.35 million baht instead by issuing 76.70 million new ordinary shares at a par value of 0.50 baht per share to the private placement.