The rheological properties of uncured rubbers mixed with different loading levels, surface areas, dispersions and structures of carbon black fillers are characterized using the ultrasonic pulse echo technique. Longitudinal wave velocity in uncured carbon black filled rubbers and longitudinal damping factor are determined at 3.5MHz frequency. Frequency-temperature superposition methods which are currently most widely used to support high frequency rheological responses are often questionable due to their limitation of possible frequency shifting ranges without multi-phases and the accuracy of shifting work itself. Thus, in order to investigate rheological behaviors over MHz, the direct ultrasonic measurements are essential. And ultrasonic characterization has a unique capability of characterizing the longitudinal property with great accuracy while most of mechanical analyzers such as torsional shear rheometry do not. Our ultrasonic pulse echo characterization results on selected rubber base materials show that (1) both longitudinal ultrasonic wave speed and damping factor increase with filler loading, and surface area and structure of carbon black filler, (2) the longitudinal acoustic properties of three different types of base rubber polymers are in the order of SBR>SBR/BR>IR, (3) both the longitudinal wave velocity and damping factor decrease with temperature, and IR (synthetic cis-1,4-polyisoprene) is the least temperature-sensitive among three base rubbers, and (4) longitudinal wave velocity increases with the material degrading while damping factor decreases.