An efficient and convenient procedure has been deve loped for the synthesis of some new tetrahydro-inde no[1,2- d]pyrimidinone 4a-h and dihydro-1H-indeno[1,2-d]pyrimidine 5a-c derivatives in high yields. Tetrahydro-indeno [1,2-d]pyrimidinone derivatives 4a-h have been synthesized by the reaction between corr esponding , cyclic ketones 1a-c, (thio) urea 2a-b and aldehyde 3a-f in the presence of Antimony(III)chloride (SbCl 3 ) in refluxing acetonitrile. Dihydro-1H-indeno[1,2-d]pyrimidine derivatives 5a-c have been synthesized by the reaction between corresponding tetrahydro-indeno [1,2-d]pyrimidinone 4a-h derivatives and alkyl bromide in ethanol. The struc tures of new compounds have been evaluated on the basis o f elemental analysis, FT- IR, 1 H NMR and 13 C NMR spectral data. They have also been screened for their antimi crobial activities.