A new fire-retardant, diethyl ethyl phosphate (DEEP), was tested as a nonflammable electrolyte solvent for dye-sensitized solar cells(DSSCs). Electrochemical measurements demonstrated that the DEEP electrolyte has a wide potential window([ 5 V), sufficient ionic conductivity (3.5 x 10(-3) S cm(-1) at 25 degrees C), and electrochemical activity for the I- / I-3(-) redox couple. The DEEP-based DSSCs exhibited an open circuit voltage of 0.72 V, short circuit photocurrent of 10.45 mA cm(-2), and a light-to-electricity conversion efficiency of 4.53%, which are almost the same as those observed from the DSSCs using currently optimized organic carbonate electrolytes. Meanwhile, the longterm stability of the DSSCs was greatly improved with the use of the DEEP electrolyte, showing a potential application of this new electrolyte for the construction of efficient, stable, and nonflammable DSSCs.