Karyotyping of mouse chromosomes is a skillful art, which is laborious work even for experienced cytogeneticists. With the growing number of mouse models for human diseases, there is an increasing demand for automated mouse karyotyping systems. Here, such a karyotyping system for mouse chromosomes based on the multiplex-fluorescence in-situ hybridization (M-FISH) technology is shown. The system was tested on a number of individual mice with numerical and structural aberrations and its reproducibility and robustness verified. Mouse M-FISH should be a valuable tool for the analysis of chromosomal rearrangements in mice.