The microwave-metal interaction pyrolysis technique has great potential of producing highly upgraded bio-oils from the biomass. In this study, the heat of the sparking metals in a microwave oven was utilized to pyrolyze the biomass into bio-oil, biogas and char. Using this technique, highly upgraded preliminary bio-oil was produced from the water hyacinth biomass. The effect of the metal type and gauge size on the product quality and composition was investigated by using different heat generating antennas. The bio-oil, obtained with each metal coil, was analyzed with Gas chromatography-mass spectrometry (GC-MS) technique. The gaseous products were characterized using spot test and combustibility analysis. Significant difference in the chemical composition of the bio-oils, produced with different metal coils, was noticed in these investigations. For all the tested metals, the oxygen and hydrocarbon content in the oil product was found significantly lower than those obtained through conventional pyrolysis. Also, unlike the thermal or thermo-catalytic pyrolysis, the bio-oil product of the microwave-metal interaction pyrolysis did not contain any water content.