Due to the development of green chemistry in recent years, researchers have been interested in the application of ionic liquids instead of common organic solvents. Ionic liquids can also apply as green catalysts. Ionic liquid have remarkable properties such as non-flammable, high thermal stability, negligible vapor pressure, easy recyclability and high solvating ability. In addition, acidic ionic liquids have made good progress in this field and can widely use in organic reactions in the mild and efficient conditions. Research in organic chemistry has expanded the one-pot multi-component reactions according to green chemistry purposes. In this work, we report the application of 3-carboxypyridinium hydrogen sulfate reported as a green, inexpensive and efficient acidic ionic liquid in the one-pot multi-component reactions. Coumarins are widely used as drug and industrial materials. We prepared here coumarins by Pechmann condensation reaction. This reaction is one of the most common procedures for the preparation of these compounds. The coumarins were prepared by the various phenols and ?-ketoesters in the presence of ionic liquid, 3-carboxypyridinium hydrogen sulfate at 110 o C under solvent- free conditions, in high yields and short reaction times. 1-Amidomethyl-2-naphthols containing1,3-amino oxygenated functional groups apply as biological compounds at drugs such as nucleoside antibiotics and HIV protease inhibitors. These compounds can be prepared by multi-component condensation of aryl aldehydes, 2-naphthol and urea/amides in acidic conditions by using 3-carboxypyridinium hydrogen sulfate under solvent-free conditions at 120 o C. The reaction has many advantages such as high yields, short reaction time, easy work-up and recyclability of the catalyst. We also used 3-carboxy pyridinium hydrogen sulfate as an acid source in Strecker reaction for synthesis of ?-aminonitriles by condensation reaction between three components containing carbonyl compound (ketone, aldehyde), amine and a cyanide source. ?-Aminonitriles are important precursors for the synthesis of ?-amino acids and other biological molecules. The reactions were carried out under solvent-free condition at ambient temperature with high yields in very short reaction times.