Magnetotactic bacteria use magnetic crystal-containing organelles (magnetosomes) to migrate along magnetic fields. Using a custom-built fluorescence microscope that combines bright-field optical and magnetic resonance imaging, the first images of magnetosomes in live Magnetospirillum magneticum cells have now been captured. Each M. magneticum cell was found to contain several magnetic nanoparticles arranged in chains that generated an average magnetic field of 5 × 10−17 Am2, consistent with previous measurements using magnetic trapping. This new technology will enable real-time imaging of nanoparticle growth in developing cells and of magnetosome chain movement during cell division.