Seashells, residues from mussel (Mytilus chilensis), Hupé 1854 processing, are an environmental load on the coasts of southern Chile. The main component of this waste is calcium carbonate, which is commonly used to neutralize soil acidity. Its application in meadows is limited due to the large quantities (tons) required. The objectives of this work were to determine the most appropriate type of mussel seashells (M. chilensis) as a source of calcium carbonate (CaCO3) for pH neutralization of an alluvial acidic soil collected from Ñuble Coast, and to identify its optimal dose. The seashell doses were optimized using response surface methodology (RSM) to achieve a soil pH close to neutral and a relatively high neutralizing power, which was defined in comparison to the pH increase achieved with commercial CaCO3. Seashells with organic matter was the most suitable formulation for increasing soil pH with a high relative neutralizing power (~ 94%), requiring a dose of 23% (w/w) to achieve soil pH values close to neutral. The fitted quadratic model explains 98.9% of variation in experimental data. This work lays the foundations for future studies aimed to find new agricultural and/or livestock applications of wastes from the shellfish industry.