Cubic FeS2 crystallites have been synthesized via a single-source approach using iron diethyldithiocarbamate as precursor under hydrothermal conditions. The sample is characterized by XRD, IR, TEM, and FESEM. The optical properties of the as-prepared FeS2 reveal that there exists a red shift compared with that of bulk materials. Meanwhile, the electrochemical properties of FeS2 demonstrate that it delivers a large discharge capacity, which might find possible application as an electrode material in lithium cells. It is also found that the reaction temperature is of importance to the formation of cubic FeS2 crystallites.