In this study, acoustic properties of carotid atherosclerotic plaques are studied ex vivo by scanning acoustic microscope (SAM). Human carotid atherosclerotic plaques were collected from patients by carotid erdarterectomy operation technique. An 80 MHz transducer was used in SAM, during the observation of the plaques. For the fibrous tissue, acoustic impedance was measured as 2.02 ± 0.06 MRayl, while for the lipid pool it was measured as 1.70 ± 0.07 MRayl and for the calcified region within the intima it was measured as 2.23 ± 0.09 MRayl. The difference in acoustic impedance values is due to the variation of elasticity within the atherosclerotic plaques. Lipid pool, together with fibrous tissue and calcified regions are the indications of vulnerable plaques, therefore, the determination of these regions within the plaques by SAM will help to evaluate the risk of thrombosis or stenosis and effect the decision making of the operations of the patients.