Catalase-like decomposition of hydrogen peroxide with the octacarboxy-phthalocyaninatoiron(III) (Fe(III)-oapc) supported on amorphous enriched rayon staple fibre (degree of crystallinity = 14%) was studied in aqueous solution at pH 7.0 and 25 degrees C. The Fe(III)-oapc supported on the rayon staple fibre is remarkably effective as an immobilized catalyst for decomposition of hydrogen peroxide. The reaction rate was analysed in terms of Michaelis-Menten kinetics, which suggests that the catalysed decomposition of hydrogen peroxide proceeds via the formation of an activated complex. Iron atom distribution of the rayon staple fibre indicated that Fe(III)-oapc existed on the fibre homogeneously. Electronic and e.s.r. spectra of the fibre suggests monomeric Fe(III)-oapc with a distorted rhombic coordinating high spin iron(III) ion. Fe(III)-oapc is considered to be immobilized by hydrogen bonding between carboxylic groups on Fe(III)-oapc and hydroxy groups of cellulose, and a weak coordination bonding of iron with hydroxy groups on cellulose. The immobilization of Fe-oapc to the rayon staple fibre extends its catalytic lifetime and makes the catalyst molecule the monomeric active state.