As the biological recognition element of microbial fuel cell (MFC) toxicity “shock” sensors, the electrode biofilm is perceived to be the crucial issue that determines the sensing performance. A carbon felt and indium tin oxide (ITO) film anode were utilized to examine the effects of anodic biofilm microstructure on MFC toxicity sensor performance, with Pb²⁺ as the target toxicant. The carbon felt anode based MFC (CF-MFC) established a linear relationship of Pb²⁺ concentration (C_Pb²⁺) vs. voltage inhibition ratio (IR_2h) at a C_Pb²⁺ range of 0.1 mg L⁻¹ to 1.2 mg L⁻¹. The highest IR_2h was only 38% for CF-MFC. An ITO anode based MFC (ITO-MFC) also revealed a linear relationship between C_Pb²⁺ and IR_2h at C_Pb²⁺ of 0.1 mg L⁻¹ to 1.5 mg L⁻¹ but better sensing sensitivity compared with the CF-MFC. The IR_2h of ITO-MFC gradually approached 100% as C_Pb²⁺ further increased. The enhanced sensing sensitivity for the ITO anode possibly originated from the thin biofilm that resulted in the efficient exposure of exoelectrogens to Pb²⁺. The employment of 2D conductive metal oxide with a smooth surface as the anode was able to increase the MFC sensing reliability in real wastewater.