Iron pyrite (FeS2) has been proved to be one of the most promising materials for counter electrodes (CEs) of dye-sensitized solar cells (DSSCs) due to its excellent electrocatalytic properties. In this report, high purity FeS2 powders were synthesized through hydrothermal method, and the effect of NaOH addition on crystal size and electrocatalytic activities of FeS2 was investigated. With the addition of NaOH, the size of FeS2 particles decreased, and the electrocatalytic activity of the FeS2 CEs and the DSSCs performance were improved significantly. Under simulated solar light irradiation with intensity of 100 mW cm(-2) (AM 1.5), the DSSCs based on FeS2 CEs with NaOH addition achieved a power conversion efficiency of 5.78%. (C) 2016 Elsevier Ltd. All rights reserved.