Abstarct: Abstract Imidazoles and dihydropyrimidines are important compounds which show a wide range of biological activities such as anti-tumor, antibacterial, anti-tuberculosis, anti-AIDS, and anti-viral. In the first part of this study, we prepared a number of substituted imidazoles by three component reaction of benzyl, aromatic aldehydes and amunium acetate in the presence of L-cystein as efficient catalyst under solvent-free condition. In the second part, various derivatives of 3,4- dihydropyrinidins were prepared by ethylacetoacetate, aromatic aldehydes and urea or thiourea in similar conditions. Use of L-cystein as an ecofriendly catalyst, solvent-free conditionary and high reaction yields are advantage of this work.