The contents of CaO, MgO, R2O3, loss of ignition, insoluble residue and the neutralization value of 29 limestones and 2 siderurgy slags employed in the neutralization of soil acidity in the State of São Paulo were determined. The results showed that most of the limestones studied belonged to the dolomitic type. The neutralization value was higher in the samples containing higher percentage of CaO plus MgO.