The influence of hydrides on the mechanism and kinetics of ductile fracture in the Zr-2.5 Nb alloy has been analyzed as a function of static tension of specimens containing 200ppm hydrogen. The smooth cylindrical specimens used were of two orientations with the maximum hydride platelet dimensions from 5 to 200 μm preferentially oriented parallel to the tensile axis. Nucleation of cracks in hydrides and internal cracks in a specimen at different deformation stages have been studied by recording the peak amplitudes of acoustic emission with a nonresonant damped sensor. The joint analysis of the stress-strain diagrams and acoustic emission results of metallographic and fractographic examinations has revealed the role of hydrides in the loss of stability by flow, neck formation and ductile fracturing under tension. Depending on the length of hydrides, two types of the ductile fracture kinetics are realized. Fine hydrides whose average size is 10 to 20 μm do not influence the stability of the plastic flow under tension, but they merely accelerate the generation of voids at the stage of ductile fracture formation. In contrast, crack nucleation in large hydrides whose average size is >60 to 100 jim is the cause of premature localization of deformation in the neck and axial decohesion in the fracture, which reduces the overall ductility of the alloy. The record of acoustic emission provided by a damped sensor shows that the signal peak amplitude and the axial crack area are proportional; this allows one to use an amplitude analysis of signals for the quantitative estimation of the dimensions of hydride-induced cracks.