In this study, fabrication and mechanical properties of internally prestressed steel I beam (strut) produced by combining steel T profile and prestressing steel plate (PSP) were investigated. While the prestressed steel plates were under various elastic tensile prestresses (ETSp), they were joined to the steel T profile by inert gas welding and then removed the ETSp on the steel plate. Prestressed steel I beams (PSIB) with 55 mm in height, 50 mm in width, 5 mm in flange thickness and 500 mm in length were fabricated by this method. The maximum permanent stress and predeflection values of fabricated PSIB due to prestressing were obtained from the beam produced by applying minimum ETSp. An increase in ETS, led to decrease in permanent stress and predeflection value of the PSIB. Flexural test results have indicated that decreasing the prestressing value resulted in an increase in the flexural capacity of PSIB. It was observed that flexural strength of prestressed steel I beam produced by this method has increased by about 30%. (C) 2006 Elsevier Ltd. All rights reserved.