In this research, the Au nanoparticle was synthesized using a biosynthesized strategy by Mentha aquatic extract and characterized by Uv-vis spectroscopic method. The synthesized Au/NPs were used as a conductive mediator for the modification of the tramadol electrochemical sensor. The modified paste electrode with Au/NPs and 1-butyl-3-methylimidazolium tetrachloroborate (BMTCB) showed high catalytic activity for the determination of tramadol in aqueous solution. When compared to the bare electrode, the Au/NPs/BMTCB/CPE increased tramadol oxidation current by 8.8 times and lowered drug oxidation potential by 20 mV. The diffusion coefficient (D) ~ 2.55 × 10− 5 cm2/s was calculated for electro-oxidation of tramadol at surface of Au/NPs/BMTCB/CPE. With a detection limit of 6.0 nM, the Au/NPs/BMTCB/CPE revealed a linear relationship between tramadol oxidation current and concentration in the range of 0.01–400.0 M.