This paper describes a simple and convenient approach to fabricate BaFe12O19 hierarchical hollow fibers or hollow fiber arrays by heat-treating electrospun solid fibers or fiber arrays using a deliberately devised two-step heat-treatment process, in which the dense shells generated in situ during the short-time pre-treatment procedure direct Ostwald ripening of flake-shaped BaFe12O19 nanocrystals in the elevated temperature heat-treatment procedure. The heat-treatment temperature has a strong effect on the structure and magnetic properties of the BaFe12O19 hierarchical hollow fibers and the resulting BaFe12O19 hierarchical hollow fiber arrays show a slight magnetic anisotropy as well as high coercivity The in situ generated dense shell-engaged directing Ostwald ripening approach reported here can be readily extended to fabricate other metal oxides hollow fibers, and the resulting BaFe12O19 hierarchical hollow fibers or hollow fiber arrays are promised to have use in a number of applications that involve microwave absorber, magnetic separation, and so forth (C) 2010 Elsevier Inc. All rights reserved.