Si/C composite anodes are of great interest for increasing the energy density of Li-ion cells. We report the applicability of the glow discharge optical emission spectroscopy (GD-OES) technique to detect and quantify the Si distribution in Si/C composite anodes. The calibration was developed in the range of 0-100 wt.-% Si by lab coated samples which are similar to real anodes. The method was verified by pristine real Si/C composite anodes with known compositions (11 wt.-% and 67 wt.-% Si) before being built into cells. Finally a first attempt of analyzing the Si/C composite anode from a commercial 18650-type cell is presented. (C) The Author(s) 2018. Published by ECS.