This study aims to determine the mechanical properties of a concrete mixture using Ground Granulated Blast Furnace Slag (GBFS) and crab shell powder as a substitute for cement and fine aggregate in a concrete mixture. The mechanical properties to be studied are concrete compressive strength, slump value and its density. As a specimen in this study, a concrete cylinder with a diameter of 100 mm and a height of 200 mm was used. The compressive strength of concrete was tested at 7, 14, and 28 days. The amount of GGBF and crab shell powder used in the concrete mix varies from 0%, 5%, 10%, 15% and 20% of cement and fine aggregate weight. The results of the study showed that combination of 5% crab shell powder and adding 10% GGBFS powder, can increase the compressive strength of the concrete of 5.56%.