Synthetic titanomagnetites (1-x)Fe3O4-xFe2TiO4, O?x?0.6) were prepared by the ceramic oxide method and the equilibrium atmosphere method, and two size fractions were separated out. The first contained particles of size >150 μm, while the second, which was ground in a water slurry, had a mean particle size of about 0.1 μm. The magnetic hysteresis properties, i.e., coercive force HC, remanent coercive force HRC, saturation, remanence JRS, JRS/JS, and initial susceptibility x0, were measured at room temperature. The coarse grain samples were found to be magnetically soft (HC~30 Oe) and the hysteretic properties independent of composition. In contrast, the fine grain samples were extremely hard (HC~400--2000 Oe) and their magnetic characteristics strongly dependent on composition. When compared with the Stoner-Wohlfarth model for single-domain magnetization, the agreement was good, indicating that these latter samples contain mainly single-domain grains. Samples containing both hard and soft fractions exhibited hysteretic properties that depended on the relative proportions of each size fraction.