Azo dyes are mutagenie pollutants and ubiquitous in the wastewater from textile, printing and food industries, thus the proper treatment of azo dye wastewater is important for global ecological security and human health.Recently, Fe0-assistant microbial remediation technology has been successfully applied in decolorization of azo dyes, yet the synergistic mechanism between Fe0 and microbe has not been well understood.To study the synergistic effects of Fe0 on azo biodecolorization, Shewanella decolorationis S12 is used as the model organism due to its high iron-reducing and azo-redueing abilities under anaerobic condition.Our study revealed a positive relationship between Fe0 dosage and azo reduction efficiency.Meanwhile two azoreductive products (1-aminenaphthylene-4-sulfonic acid and 1-aminenaphthylene-2-hydroxy-3, 6-disulfonic acid) significantly decreased when Fe0 participating into the biodecolorization.Besides that, reinforcement of bacteria activities (characterized by cell morphology and Live/Dead ratio) were observed in bioazoreduction containing Fe0.Additionally, iron complexes adsorbing onto the bacterial surface examined by transmission electron microscope energy dispersive spectroscopy (TEM-EDS) analysis, proved the direct interaction between metal and bacteria.In a word, Fe0 can strengthen the ability of iron-reducing bacterium to actively adsorb iron complexes, resulting in the increase of the decolorization efficiency and further degradation of azo reduction products.This work sheds light on synergistic interactions between Fe0 and iron-reducing bacterium and provide theoretical guideline for application of Fe0-assistant microbial remediation technology on degrading and detoxifying azo dyes wastewater.