The aim of the study is to investigate the effect of periwinkle shell filler (PSF) as an additive on the compressive strength of lateritic blocks. Physical tests on the filler indicated a specific gravity of 2.75; loose and compacted block densities of 2378.47 kg/m3 and 3102kg/m3 respectively, while a porosity of 23.26% was recorded. The lateritic soil met the requirements for use in block production. The soil blocks were produced by replacing the quantity of the laterite with the filler in the percentages of 0, 1.5, 2.5, 3.5, 5, 6.5, 7.5, 8.5 and 10% by volume. A total of 135 blocks of dimension 210mm × 100mm × 100mm were prepared for compressive strength, density and water absorption tests at 7, 14 and 28 curing ages. The results of the test revealed a higher compressive strength values of 1.06, 3.22 and 2.98 N/mm2 were recorded at 7,14 and 28 days respectively with an optimum percentage replacement level of 5% beyond which the strength starts to decline. It was also observed that, the strength development could not continue beyond 14 days an indication that the filler lacks silicate compound to enhance continuous strength development. It is therefore concluded that the filler needs to be blended with cement to be an effective stabilizing agent.