An experiment was conducted in order to: (1) assess equine cortical bone status in vivo by quantitative ultrasonography (QUS); (2) evaluate certain mechanical properties of the third metacarpal bone (McIII) and to characterize its regional variation along the bone; and (3) compare the in vivo results with the ex vivo mechanical tests on the same bone. Eight adult mares were assessed with a QUS device on the mid-section of the right McIII (dorsal and lateral regions). Cortical bone samples from the dorsal and lateral regions of both McIII were collected post-mortem, and tested in compression and bending. Values of speed of sound (SOS) on the lateral region were higher than for the dorsal one (P<0.0001), but they were linearly correlated (r=0.803; P<0.05). In compression, the maximum stress (σmax) was influenced by bone region and bone section, and an interaction was found between these two effects (P<0.01). Samples from the dorsal region were stiffer than samples from the lateral region (P<0.0001), and lower values of the Young’s modulus (E) were obtained on the McIII distal sections (P<0.05). Lower bending strength was observed in the distal section of the bone, when compared with the proximal and the mid-section (P<0.01). In vivo SOS measurements on the dorsal region were highly correlated with the E obtained from ex vivo compression tests (r2=0.92; P=0.0002). These results suggest that QUS could be used as a non-invasive method in the assessment of equine cortical bone mechanical properties.