Cubic spinel MnFe2O4 nanoparticles were synthesized using a simple hydrothermal method followed by post-annealing. The effects of the reaction temperature on the crystallinity, morphology, and electrochemical performance were studied. The reaction temperature played an important role in the synthesis of highly crystalline MnFe(2)O4 nanoparticles. At low reaction temperatures (<160 degrees C), the synthesized product contained a secondary inactive Fe2O3 phase as well as MnFe2O4 nanoparticles. In contrast, pure MnFe2O4 nanoparticles were obtained at temperatures above 180 degrees C. Furthermore, the crystallinity of the MnFe2O4 nanoparticles was enhanced significantly by increasing the reaction temperature to 200 degrees C. The cubic spinel MnFe2O4 nanoparticles synthesized at 200 degrees C delivered a maximum specific capacitance of 282.4 F g(-1) at a current density of 0.5 A g(-1) in a 2 M aqueous KOH solution, and exhibited long-term cyclic stability of 85.8% capacitance retention after 2000 cycles. This was attributed to the cubic spine! ferrite nanocrystallite particles not only providing the more active sites for OH- ion diffusion but also reducing the path lengths for OH- ion diffusion. These results show that the synthesized MnFe2O4 nanoparticles are promising candidates for pseudocapacitors and other electrochemical applications. (C) 2017 Elsevier B.V. All rights reserved.