Co–Ti substituted M-type hexagonal barium ferrite nanoparticles BaFe12-2xCoxTixO19 (0≤x≤1.0) have been prepared by a sol-gel method. Magnetic and structural properties of the powders were characterized with a Mössbauer spectroscopy, vibrating sample magnetometer, x-ray diffraction (XRD), thermogravimetry (TG), and differential thermal analysis (DTA). The decomposition of amorphous hydroxides in the dried precipitate continued until 570 °C, according to a TG-DTA analysis. The result of XRD measurements shows that the a and c lattice parameters increase with increasing x from a=5.882 and c=23.215 Å for x=0.0, to a=5.895 and c=23.295 Å for x=1.0. The 57Fe Mössbauer spectra were fitted by a least-squares technique with four subpatterns of Fe sites in the structure and corresponding to the 4f2, 4f1+2a, 12k, and 2b sites. The relative spectra areas of BaFe10CoTiO19 at 295 K were 15%, 30%, 50%, and 5% for 4f2, 4f1+2a, 12k, and 2b subspectra, respectively. The 2b site had a very large quadrupole splitting. The isomer shifts indicated that the valence states of the Fe ions were ferric. The magnetization slightly decreases and the coercivity, HC, drops dramatically from about 5014 to 228 Oe as x increases from 0.0 to 1.0. Co–Ti substituted barium hexaferrit- e to be controlled to reduce their coercivities with a small decrease of their magnetization. © 2002 American Institute of Physics.