Abstract The textural and structural characteristics of four CO 3O 4 samples of different prehistory are compared. Cobalt hydroxide and oxyhydroxide are used as parent compounds being transformed in the spinel by thermal and mechanical treatments. The main differences between samples are a higher content of microstrains for those derived from Co(OH) 2 and the presence of a porous system in thermally decomposed samples which is absent in the materials obtained by grinding procedures. These parameters affect the catalytic activity of the samples in the H 2O 2 decomposition reaction. An enhancement of the activity is observed for ground samples, particularly for ex-Co(OH) 2 Co 3O 4.