The solid-solid interactions between nanosized pure and NiO-substituted ferric and titanium(IV) oxides have been investigated using XRD technique and microstructure studies, also magnetic properties were studied using vibrating samples magnetometer (VSM). The amounts of substituting Ni2+ were x = 0, 0.2, 0.4, 0.6, 0.8 and 1 mole. A mixture equimolar proportions of finely powdered Fe2O3 and TiO2 were mixed with NiO, ball milled, compressed at 250 kg/cm(2) and fired at 1200 degrees C for 4 h. The obtained results showed that with substituting Ni2+ concentration x = 0 only Fe2TiO5 phase is present (similar to 80 nm) which showed a very small saturation magnetic flux density (B,), remnant magnetic flux density (B,) and the maximum energy product (BH)(max). By the addition of x = 0.2 NiO, new phases were observed NiTiO3 and NiFe2O4 of crystallite sizes 160 and 110 nm, respectively. By the increase of substituting Ni2+ concentration the NiTiO3 and NiFe2O4 phases increased on the expense of Fe2TiO5 up to x = 0.4, then the increase in substituting Ni2+ concentration led to a decrease in Fe2TiO5 and NiTiO3 while NiFe2O4 increases which results in a great improvement of magnetic properties. All samples exhibit a catalytic activity towards H2O2 decomposition and the values of rate constant increase with increasing amount of Ni2+ substituting. The most acidic active sites are shown by specimens substituted with x = 0 this concludes that H2O2 decomposition is not favored on acidic active sites. (c) 2006 Elsevier Ltd. All rights reserved.