Summary form only given. In the last few years, several authors have reported the observation of a new class of acoustic waves in sub-wavelength diameter tapered optical fibers (TOFs) through Brillouin scattering [1, 2]. These include the observation of surface acoustic waves (SAW), hybrid shear and longitudinal acoustic waves (HAW) associated with anti-crossings (AC). It has also been suggested that these acoustic waves could be used to develop compact Brillouin optical sensors based on TOFs.Here we report the first tensile strain measurement of TOFs using Brillouin spectroscopy. Because of the hybrid nature of the acoustic modes, we show that the backward Brillouin response to strain in those tiny waveguides is fundamentally different compared with that of conventional single-mode fibers (SMFs) [3,4]. More specifically, we measured a strain coefficient for SAWs two times lower than theoretically predicted. Figures 1 (a) shows the experimental setup for measuring the Brillouin spectrum in the fiber taper schematically depicted in Fig. 1(b), and tapered using the heat-brush technique [1]. The backscattered Brillouin spectrum was measured using a heterodyne detection and an electrical spectrum analyzer. Strain was applied by further stretching the fiber taper using two programmable translation stages.