A novel electrolyte applied in electrochemical double-layer capacitors (EDLCs) has been prepared based on lithium hexafluorophosphate (LiPF6) and acetamide and subsequently characterized by differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), electrochemical techniques and so on. The mixtures of LiPF6 and acetamide at the molar ratios of 1:4 to 1:6 exist as liquids below 25°C, which is attributed to the melting point depression of mixture and the coordination of the polar groups (CO and NH groups) of acetamide with Li+ and PF6 − ions. The strong interaction between LiPF6 and acetamide results in the rupture of the electrovalent bond of LiPF6 and the breakage of hydrogen bonds among the acetamide molecules, leading to the formation of a liquid electrolyte. The LiPF6/acetamide electrolyte with a molar ratio of 1:5.5 exhibits a 5.2V electrochemical window and suitable ionic conductivity at room temperature. In particular, the coin-type cells with carbon electrodes and LiPF6/acetamide electrolyte possess high thermal stability and electrochemical properties, showing that the as-prepared LiPF6/acetamide electrolyte is a promising candidate for EDLCs.