Motivation: Mathematical morphology provides many powerful operators for processing 2D and 3D images. However, most mathematical morphology plugins currently implemented for the popular ImageJ/Fiji platform are limited to the processing of 2D images. Results: The MorphoLibJ library proposes a large collection of generic tools based on mathematical morphology to process binary and grey-level 2D and 3D images, integrated into user-friendly plugins. We illustrate how MorphoLibJ can facilitate the exploitation of 3D images of plant tissues. Availability: MorphoLibJ is freely available at http://ijpb.github.io/MorphoLibJ/ Contact: david.legland@nantes.inra.fr Supplementary information: Supplementary data are available at Bioinformatics online.