Fe–Zr nanocrystalline alloys with an as-milled grain size less than 10nm were synthesized by ball milling. The microstructure changes due to annealing were characterized using X-ray line broadening, microhardness, focused ion beam channeling contrast imaging, and transmission electron microscopy (TEM). Additions of 1/3 to 4at.% Zr stabilized nanocrystalline grain sizes at elevated annealing temperatures compared to pure Fe. With 4at.% Zr, a fully nanocrystalline microstructure with a TEM grain size of 52nm was retained at temperatures in excess of 900°C. Alloys with lower Zr contents showed less stability, but still significant compared to pure Fe. Bimodal nano–micro grain size microstructures were also observed.