We developed a sensitive and cost effective sensor based on highly conductive and adsorptive biochar nanoparticles for electrochemical detection of 17 beta-estradiol. The biochar is ubiquitous and has the advantages of large specific surface area, cost effectiveness, and good stability, which has the potential to be utilized for electrode construction as long as the conductivities are guaranteed. We obtained nano sized biochar particles (BCNPs) and investigated electrochemical properties of the BCNPs with variation of the pyrolysis conditions. BCNPs with high conductivity (BCNP800) were obtained and utilized for reproducible and stable electrochemical sensor construction. The produced highly conductive BCNP800 sensor had exhibited improved amperometric responses such as decreased impedance, lowered anodic potential and enhanced current signal toward 17 beta-estradiol compared with the pristine glassy carbon electrode. In addition, the adsorption-accumulation by BCNP800 for 17 beta-estradiol resulted in great sensing signal amplification. With synergetic effect of high adsorption and conductivity properties of the BCNP800 sensor a detection limit of 11.30 nM was obtained. The accuracy and reliability of the BCNP800 sensor were confirmed to be compatible with the high performance liquid chromatography analysis and it could be successfully applied for real environmental water analysis. (C) 2018 Elsevier Ltd. All rights reserved.