Microbial fuel cells (MFCs) are considered as power generation devices for sustainable energy. However, the power generated is insignificant compared to other energy production devices. In this study, a mini autonomous biosensor (MAB) based on MFCs has been designed for detecting hazardous hexavalent chromium in wastewater. Hexavalent chromium has been classified as a human carcinogen causing serious birth defects due to its mutagenic and teratogenic properties. The power generated by the MAB has been investigated to study the feasibility of providing power to itself. In addition, electrochemical analyses of conductive silver paste and carbon cloth as the anode were conducted in the MAB for detecting hexavalent chromium in the anode chamber. Results show that a maximum voltage of 518.17 mV and a power density of 1.075 mW/cm(2) could be achieved using carbon cloth with an external resistance of 1000 omega, while a higher limiting current density of 0.015 mA/cm(2) could be achieved with conductive silver glue as the anode electrode. Besides, the voltage output of the MAB decreased rapidly with the addition of hexavalent chromium into the wastewater. Also, the recovery time for the MAB was much shorter than found in previous studies. The MAB demonstrated potential for simultaneous production of electricity and detection of hexavalent chromium, which would open up avenues for autosensing applications in the environment as well as smart powering devices. Results indicate that the MAB with conductive silver glue as anode electrode is feasible for detecting hexavalent chromium in wastewater.