Recovery of precious metals from waste is important in terms of resource security and environmental prevention. Leaching is an essential step in hydrometallurgy. Microwave irradiation was used as one of the methods to accelerate the leaching rate and efficiency. However, because the dielectric constant of the commonly used leachate is high, most of the microwave energy is not properly transmitted to the target waste. To overcome this limitation, we propose ionic liquids with a low dielectric constant as an alternative leaching agent. Ionic liquids are known to be environmentally friendly due to their low vapor pressure and high thermal stability and composed of only ions, leading to high solubility in metal ions. Thirty kinds of hydrophobic ionic liquids were chosen from among numerous candidates according to the dielectric constants which are estimated using a linear free energy relationship model with in silico calculated descriptors. Among them, trioctyl-methylammonium chloride was selected because its dielectric constant is the lowest (ε = 9.0). The ionic liquid along with organic acid as an additive was used for microwave leaching of platinum group metals from spent automotive catalysts. As a result, the leaching efficiencies of Pd(II) and Pt(IV) within 1 hour were 95.7±1.5% and 88.3±1.1%, respectively, which are similar to leaching performance using aqua regia. The proposed leaching method is expected to have great potential as a green urban mining technology without using highly toxic acids and organic solvents.