Excessive usage of materials is causing fast depletion of natural stone deposit. This study therefore investigates the performance of palm kernel shells (PKS) and periwinkle shells (PS) as alternatives coarse aggregates in concrete. Forty cubes and 40 cylinders each were produced with PKS and PS as replacement materials for granite. Series of tests were conducted to determine their performances. The results showed that, compressive and tensile strengths decrease as PKS and PS content increases, which allow specific area to increase, thus requiring more cement paste to bond effectively with the shells. The result also revealed that for all curing ages, palm kernel shell concrete (PKSC) have lower compressive strength and tensile strength than periwinkle shell concrete (PSC). The compressive strength and tensile strength of the 28-day PKSC with 100% replacement were 4.33 N/mm2 and 3.68 N/mm2 respectively; that of PSC at 100% replacement were 5.89 N/mm2 and 4.95 N/mm2 respectively; and granite concrete without any replacement were 25.11 N/mm2 and 11.74 N/mm2 respectively. It is concluded that both PKSC and PSC satisfied the compressive strength and tensile strength requirement of light weight concrete, although PS has better gradation and bonding to cement than PKS. This implies that PS is best suited as replacement for granite in lightweight concrete than PKS. It is recommended that the mix-ratio should be altered to get higher values of compressive strength; and both PKS and PS should be used for lightweight concretes.