We investigated the mechanism of single-bubble fragmentation during mechanical stirring under different trailing vortex conditions. Experiments and numerical simulations using the LES-VOF method were carried out under different bubble sizes and locations of bubble injection. We found that the following three phenomena can cause bubble fragmentation: collision with impeller blade; shear stress in the boundary layer ahead of the impeller blade; and interaction between trailing vortices and the bubble. In the last case, the mechanism of fragmentation can be categorized into six types, which are determined by the relationship between the bubble behavior and the trailing vortices. Thus, we clarified the relationship between trailing vortices and bubble fragmentation for the first time in a stirred vessel. (C) 2019 Elsevier Ltd. All rights reserved.