RbFeF3is a transparent ferromagnet (below 87°K) with a large Faraday rotation which permits the direct observation of magnetic domain structures in bulk crystals. An etch‐pitting solution has been developed which reveals the dislocation configuration existing in the crystals, and it has been demonstrated that RbFeF3exhibits sufficient plasticity so that arrays of dislocations can be put into crystals. The role of dislocation subboundaries and slip bands as nucleation sites for reversed magnetic domains will be demonstrated. The effectiveness of subboundaries and slip bands as pinning sites for domain walls when subjected to varying dc and ac magnetic fields are discussed.