Cu-substituted strontium-hexaferrites with chemical compositions SrFe12-xCuxO19 (0 <= x <= 0.8, x = 0, 0.2, 0.4, 0.6 and 0.8) were synthesized successfully by the tartrate-gel route, followed by calcination at 850 degrees C for 2 h. All the Cu-substituted compositions have single phase with hexagonal crystal structure and P6(3)/mmc space group, but parent compound shows a small amount of hematite impurity phase. This suggests that introduction of Cu helps in reducing the calcination temperature to obtain a single phase compound. Furthermore, all the samples are nanocrystalline in nature with average crystallite size ranging from 40 to 50 nm. The variations in the magnetic parameters with increase in the copper content in the Sr-hexaferrite structure indicate the occupation of Cu at octahedral interstitial site. The above nanocrystalline-hexaferrite powders were employed as catalysts for the reduction of 4-nitrophenol to 4-aminophenol, in aqueous medium. The progress of the catalytic reaction was examined by UV-visible absorbance spectroscopy at different intervals of time. The results indicated that the parent compound (SrFe12O19) was catalytically inactive, while all other Cu-substituted samples exhibited good catalytic activities in transforming 4-nitrophenol into 4-aminophenol. Our results reveal that the catalytic property could be induced in Sr-hexaferrite samples by Cu-substitution at octahedral site. (C) 2020 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.