<p>Enhancing the depth-to-diameter ratio in micro deep-hole is crucial in electrical discharge drilling (EDD). Using deionized water as a dielectric rather than kerosene-based oil can effectively improve the material removal rate and reduce electrode wear. However, discharge-generated debris adheres to the electrode surface when drilling using deionized water. This narrows the flow path through which bubbles and debris escape from the interelectrode area, thereby hampering the dielectric circulation. Consequently, the drilled hole diameter increases, while and the machining accuracy decreases. This study aims to elucidate the debris adhesion mechanism. Here, we experimentally investigated the adhesion behavior of debris and its relationship with electrode polarity. Based on the analysis results of the debris and electrode surface elements, we investigated the redox phenomenon occurring between the electrodes during discharges and discussed the mechanism of the debris adhesion in EDD process.</p>