This article provides an overview of the authors' activity on organic secondary ion mass spectrometry (organic SIMS) using ionic liquids. Ionic liquids, i.e., molten salts with a melting point less than 100℃, have negligible vapor pressures, so that they are compatible with ultra-high vacuum. They are divided into two groups : aprotic ionic liquids and protic ionic liquids. Both ionic liquids were tested as liquid matrices and as primary ion beams in organic SIMS. Protic ionic liquids proved to be effective to enhance molecular secondary ion intensities, whereas aprotic ionic liquids were not useful. Among ionic liquids, alkylammonium titrates such as propylammonium nitrate will be most promising for organic SIMS.