In this study, the magnetic properties of magnetosomes isolated from lyophilized mag-netotactic bacteria Magnetospirillum caucaseum SO-1 were assessed for the first time. The shape and size of magnetosomes and cell fragments were studied by electron microscopy and dynamic light scattering techniques. Phase and elemental composition were analyzed by X-ray and electron diffraction and Raman spectroscopy. Magnetic properties were studied using vibrating sample magnetometry and electron paramagnetic resonance spectroscopy. Theoretical analysis of the magnetic properties was carried out using the model of clusters of magnetostatically interacting two-phase particles and a modified method of moments for a system of dipole–dipole-interacting uniaxial particles. Magnetic properties were controlled mostly by random aggregates of magne-tosomes, with a minor contribution from preserved magnetosome chains. Results confirmed the high chemical stability and homogeneity of bacterial magnetosomes in comparison to synthetic iron oxide magnetic nanoparticles.