Abstarct: Due to the growing trend of using nanomaterials in the manufacture of chemical sensors in recent years, in this project, the performance of a glass carbon electrode modified with multi-walled carbon nanotubes and gallic acid-capped gold nanoparticles (GA-AuNPs / MWCNTs / GCE) was used for the online measurement of Chromium (VI) using continuous flow injection (FIA) and an amperometric detector. The behavior of various modified electrodes was compared in this study. The addition of multi-walled carbon nanotubes significantly improved the repeatability and sensitivity of a glass carbon electrode modified with gallic acid-capped gold nanoparticles. Several parameters such as the density of carbon nanotubes, the drop volume of gallic acid-capped gold nanoparticles, the pH, the volume and type of carrier electrolyte (buffer), the ionic strength, the voltage applied to the sensor, the flow rate of the carrier electrolyte, and the injected volume of the sample are optimized. Under the optimal conditions, this sensor demonstrated a broad linear range in two zones of 2×10-4 to 2×10-2 μM and 2×10-2 to 11.5 µM, with a detection limit of 87.85 pM. Also, the influence of varied ion interference on sensor performance was explored, and the results revealed high selectivity of the sensor. The proposed method was effectively applied for measuring the concentration of chromium (VI) in various water samples.