We studied mechanical properties and alloy effects of free-standing aluminum microbeams (50 × 500 × 2 μm) in a piezo-actuator-driven test apparatus with a load resolution of ±0.2 mN and a displacement resolution of ±10 nm. Pure Al and Al-2%Ti microbeams were fabricated using micromachining techniques. In tensile tests, we found the yield strength to be approximately 120 MPa for the pure Al beams, and approximately 75% higher for the alloyed beams. We examined the results with respect to those of bulk materials and thin films adhered to substrates. In stress relaxation tests, we observed a load drop of 56% over 10 min for the pure Al beams. We attributed this to grain boundary sliding and the nature of a free-standing thin film, i.e., the absence of a substrate. For the alloyed beams, the load drop was only 16%. We believed the difference was due to Al3Ti precipitates formed at grain boundaries, which hindered dislocation movements. We used TEM to reveal the microstructural features of the microbeams.