Directly obtaining pristine magnetic silk fibers from silkworm

•A pristine magnetic silk fiber was directly obtained from silkworm.•This MSF has enhanced mechanical properties than the normal SF.•This MSF has enhanced thermal stability than that of the normal SF. By feeding the silkworms with the nano Fe3O4 powder together with mulberry leaves, we directly obtained silkworm spun pristine magnetic silk fiber, MSF. To compare with the normal SF found that this MSF not only has expected magnetic properties, but also has enhanced thermal stability and mechanical properties, e.g. stress and strain.