Hiroshi SAITO and Satoshi OSAWA This study aimed to clarify the effect of the atmospheric plasma pressure treatment condition on the interfacial bonding of the carbon fiber (CF)/polypropylene (PP) composites. Here, both the CF and PP were modified using the atmospheric plasma pressure treatment. The PP surface was modified under the processing electric power of 20 W and processing time of 30 s. The CF surface was modified under the elevated processing electric power and time. The apparent interfacial bonding strength was evaluated by the tensile strength perpendicular to the fiber direction. As a result, the effect of the atmospheric plasma treatment employed in this study on the properties of PP was limited, whereas the surface of CF was damaged under the processing electric power of 20 W, resulting in the decrease of the apparent interfacial bonding strength of the CF/PP. In addition, the apparent interfacial bonding of the CF/PP tended to increase and the decrease with the increase of the processing time, indicating that the trade-off relation between the surface modification and damaging would decide the interfacial bonding of the Cf/PP. Finally, the possibility of the superposition formulation between the processing electric power and the processing time was discussed.