Biodiesel is the best alternative fuel to Petroleum Diesel, as it is renewable and environmental friendly. The attenuation of ultrasonic waves of fixed frequency of2 MHz for two commercially available biodiesels, Cotton Seed Oil Methyl Esters (CSOME) and Palm Stearin Methyl Esters (PSME) and their blends with Petroleum Diesel (PD), were studied using an ultrasonic interferometer after long – term storage of two years. Between the two biodiesels, CSOME is rich in unsaturated Fatty Acid Methyl Esters (FAME) and the PSME in saturated FAME. The results showed that there was distortion in the amplitude variation of ultrasonic waves and indicates the presence of insoluble particles due to scattering of ultrasonic waves. The two biodiesels and blends followed a specific trend of amplitude distortion. The ultrasonic absorption estimated was found to be lower than fresh biodiesels and blends except for 30 %, 40 % and 50 % volume blends of PSME biodiesel for which ultrasonic absorption was more than the corresponding fresh blends. The percentage of changes in ultrasonic absorption was in the range 56.92 to 95.86 for stored CSOME blends.For PSME blends the corresponding range was 45.71 to 121.53.The change in ultrasonic absorption for PSME blends was sharp when compared to CSOME blends. The net ultrasonic attenuation is majorly due to scattering. The nature of scattering was different for both the biodiesels and blends that were reflected in amplitude distortions. Ultimately, it was concluded that the ultrasonic attenuation strongly depends on fatty acid profiles of biodiesels.