The mechanical behavior of titanium-based alloy Ti6242S was investigated under uniaxial tensile loading at 723 K (450 °C) and 823 K (550 °C) under air and argon environments. Microtensile specimens ranging from 1 mm to 100 µm in thickness were tested to investigate the influence of the decrease in thickness on mechanical properties. Fractographic analyses were carried out using scanning electron microscopy. At 450 °C and 550 °C, a decrease in yield strength, ultimate tensile strength, and strain-to-failure with decreasing thickness was observed. These drops in the macroscopic tensile properties of the thinnest specimens result from a combination of oxidation, which further impairs the specimens with a high surface-to-volume ratio, and the overall lower number of colonies of α lamellae contained in thinner specimens. Ti6242S exhibited dynamic strain aging at 450 °C, especially in specimens with thickness below 500 µm.