The feed rate at which a defect free friction stir weld can be run (friction stir weldability) on an HSLA steel plate can vary widely between heats that meet the same specified physical properties. Consequently, every time a new heat of HSLA steel is obtained, exploratory welds must be run to determine the proper feed rate for that plate. Previous research suggests that the varying levels of alloying elements related to high temperature physical properties between the different heats causes the observed change in friction stir weldability. Because of this, it was hypothesized that the high temperature physical properties of HSLA steels are related to their friction stir weldability.High temperature physical propeties of HSLA steels are a function of the alloying content of the steel. To determine the relationship between high temperature physical properties and alloying content, eight different heats of HSLA steel with different chemical compositions were obtained. In particular, percent additions of molybdenum, vanadium, niobium, and titanium were varied between the heats in a factorial design. Gleeble compression tests were run on each heat to determine their high temperature properties. Based on these tests, experimental models wereconstructed to estimate the high temperature properties of HSLA steels based on composition and temperature. These models were used to determine the high temperature physical properties of HSLA heats with known friction stir weldability. The high temperature physical properties werecompared to the friction stir weldability of each heat. No correlation was found in this study between the high temperature properties examined and friction stir weldability in HSLA steels.