The high temperature deformation characteristics of a commercial beta-titanium alloy Ti-3Al-8V-6Cr-4Mo-4Zr have been studied in the temperature range 830-925 degrees C. The alloy exhibited superplasticity in a narrow temperature and strain rate range i.e. 850-865 degrees C and 5 x 10(-5) -3 x 10(-3) s(-1)supercript stop respectively, with a maximum elongation of 634% at 855 degrees C. The superplastic behaviour in the alloy is considered to arise as a result of subgrain formation at the higher strain rates (region III) which enhances diffusional creep at lower strain rates (region II). The activation energy values for regions II and III were found to be close to the lower of the two activation energy values (129.2 KJ/mole) proposed to describe self diffusion in beta-phase suggesting that the rate controlling mechanism during high temperature deformation of the alloy was that for lattice diffusion. (c) 2005 Springer Science + Business Media, Inc.