Tensile properties and deformation-fracture behavior at temperatures ranging from 123K to 293K of a Ti-6Al-4V alloy sheet with a thickness of 1.5mm has been studied, and the effects of testing temperature, specimen orientation and heat-treatment were investigated. An increase in strength and a decrease in fracture strain were found with decreasing tension temperature, and the anisotropy in tensile properties was observed at room and cryogenic temperatures both in the annealed and solution treated and aged (STA) specimens. TEM examinations indicated that plastic deformation occurred within both α and β phases in the STA specimens testing at either room or cryogenic temperature. The dominant deformation mechanism varied from dislocation slip at room temperature to twinning at 123K. SEM observations showed that the amount of dimples and tearing grains on fractured surfaces of the specimens decreased as testing temperature was decreased.