Heavy metals from mining sites can contribute to adverse health and environmental issues. Conventional liming practice depletes natural limestone deposits. Blood cockle shell (BCS) and palm kernel shell (PKS) calcination produced alkaline ash to immobilize heavy metals in soil. This study investigates the acid neutralizing capacity (ANC) of calcined BCS and PKS composites. BCS and PKS composites were prepared at various weight ratios (i.e. 1:0, 1:1, 1:5, 1:10, and 0:1) and were combusted for 1 hour at 400°C and 900°C, respectively. BCS and PKS composites were determined by its yield, pH, and ANC. The combustion characteristics for composites was conducted using thermogravimetric analysis (TGA). Elemental analysis was conducted using X-ray fluorescence (XRF) spectroscopy. Fourier transform infra-red (FTIR) was conducted for functional groups analysis. Ash content of composites increased when the portion of PKS feedstock is decreased. Increasing combustion temperature from 400°C to 900°C reduced the ash contents. The pH of raw and combusted composite (at 400°C) decreased as the portion of PKS feedstock is increased. Calcined composites at 900°C have slightly different pH value except for 0:1 sample. ANC value increased as PKS portion in composites reduced. Higher content of calcium oxide (CaO) in the composites increased the ANC value.