The present invention relates to solid base catalysts consisting of an amorphous material obtained from a silica or alumina gel containing an alkaline, earth-alkaline or transition metal (M), characterized by a molar ratio between metal (M) and Si or Al ranging from 30:1 to 0.0001:1, a surface area ranging from 100 to 600 m.sup.2/g, an overall pore volume ranging from 0.1 to 1.1 ml/g, an average channel diameter ranging from 30 to 150 .ANG. and a density of the base sites ranging from 10 to 900 .mu.mol/g. Said catalysts can be conveniently used in base catalysis reactions.