The performance of 2-Mercapto-5-benzimidazolesulfonic acid (MBIS) in a Watts bath in crack electro-healing was investigated. Potentiostatic and galvanostatic voltammetry, current efficiency measurements were performed for electrochemical investigation. The morphology of the healed crack indicates that the healing crystals grow in a controllable manner with the addition of MBIS under forced convection with the healing crystals fill preferentially in the crack tip to the crack sidewalls. No obvious defects were observed along the interface between the substrate and the healing crystals, which is attributed the much higher current efficiency of MBIS. Annual-ring like defects are observed but with a much longer width compared with PEI. The formation mechanism of annual ring is discussed. Possible approach to get defect-free crack healing is also prospected. (C) 2015 The Electrochemical Society. All rights reserved.