A series of ethene/propene/CO terpolymers (PEPCO) with different ethene/CO (ECO) contents has been prepared and physically characterized. The ECO content varies between 0 and 80 wt%. Dielectric investigations have been carried out over wide ranges of frequency (10(-1)-10(6) Hz) and temperature (-65 to 60 degrees C). In addition, differential scanning calorimetry (DSC) and stress-strain measurements have been done. The dielectric results showed that all samples exhibit three or more relaxations, namely; local, glass and high-temperature process. The relaxation strength of the local process is found to increase with increasing the ECO contents and is attributed to the ECO blocks. DSC showed that the glass transition temperature decreases with increasing ECO content and varies between 3 and 23 degrees C. The composition dependence of the glass temperature, T-g, follows a Fox behavior. In addition, DSC measurements showed an endothermic process with multiple peaks in the range 30-150 degrees C. The heat of melting increases slightly with increasing ECO content. The stress-strain behavior is similar to thermoplastic rubber for samples with ECO contents lower than 50 wt%.