High viscosity and cost limit the performances and applications of hypergolic ionic liquids as propellant fuels. In this paper, several highly viscous hypergolic ionic liquids were prepared and mixed with low-cost ethanol in different proportions. These mixtures were tested by dropping them into an oxidizer, and their ignition delay time was obtained by a high-speed camera. The molecular dynamics simulations were applied to explore the microstructure and ionic interactions of mixtures. The results indicated that the viscosity was significantly reduced at a low mole fraction of ethanol (x(ethanol)), and the maximum deviation was shown at x(ethanol )= 0.3 for most ionic liquids. Molecular dynamics simulations suggested that ethanol destroyed and weakened original interactions between anions and cations and, therefore, enhanced their diffusivity and mobility in mixtures, which caused a significant decrease in viscosity. The ignition tests indicated that mixtures with a proper amount of ethanol usually showed a shorter ignition delay time than the pure ionic liquids, which confirmed the important role of viscosity on the ignition process. Our studies suggest that mixing with a proper amount of small-molecule liquid is a acceptable strategy for improving ionic mobility and ignition performances of hypergolic ionic liquids.