The biodiesel content or blending ratio of a biodiesel fuel is crucial for the quality control and official regulation. A rapid (<10 s) and simple analytical method for estimating the blending ratio of biodiesel had been developed based on electrochemical impedance spectroscopy (EIS) with a low cell constant (0.0408 cm (1)) detection chamber composed of a hydrophobic electrode pair (two identical screen-printed carbon paste electrodes) to improve the data precision. In low frequency region (<1 Hz), the impedance response (CV < 3%, n = 8) was useful to estimate the blending ratio of biodiesel (r(2) > 0.98) with good resolution, reproducibility and thermal stability, which is important for the quality control and regulation of the eco-friendly fuel. (C) 2012 Elsevier Ltd. All rights reserved.