Shellfish on Randusanga Beach, Brebes have not been widely used. Shellfish contain pozzolanic chemical compounds that can be used as a substitute for concrete forming materials. This research is an experimental study to determine the concrete compressive strength uses 15x15x15cm dimensions cube-shaped specimens for normal concrete and cylindrical specimens with a diameter of 15cm and a height of 30cm for shellfish mixed with variations of 0%, 3%, 5%, 10% and 15%. Testing on concrete compressive strength is carried out at 28 days. The results of the study show that concrete in shellfish proportion of 15% mixture has increased to 16% of normal concrete. So based on this study it can be concluded that the greater proportion of shells will increase the concrete compressive strength.