A study was made on the hydroxylation of six macrocyclic bicopper complexes withbridge of SCN~-, Cl~-, Br~-, I~-, N_3~- or OH~- respectively in aqueous solution. Electronic spectra anddata of titration by ion selective electrode show that the basic structure of the complexes remainedunchanged during hydroxylation and hydroxyl group bound to copper atom only at the axial directionof the complexes, pH titration was made by auto-titration and data acquisition system controlledby microcomputer. Data of pH titration was pq-analysed by program LEMIT which show that1-4 hydroxyl groups bind to copper atom stepwisely. Tweuty four stepwise hydroxylation constantsof the complexes were calculated and concentration distribution of various species during pH chang-ing and hydroxylation were obtained. The six complexes except that with bridge N_3~- formed dihy-droxo-complexes mainly at about pH 9 and formed monohydroxo-complexes mainly at about pH7.5. A study was made on the hydroxylation of six macrocyclic bicopper complexes with bridge of SCN ~ -, Cl ~ -, Br ~ -, I ~ -, N_3 ~ - or OH ~ - in aqueous solution. Electronic spectra and data of titration by ion selective electrode show that the basic structure of the complexes remainedunchanged during hydroxylation and hydroxyl group bound to copper atom only at the axial directionof the complexes, pH titration was made by auto-titration and data acquisition system controlled by microcomputer. Data of pH titration was pq-analysed by program LEMIT which show that 1-4 hydroxyl groups bind to copper atom stepwisely. Tweuty four stepwise hydroxylation constants of the complexes were calculated and concentration distribution of various species during pH chang-ing and hydroxylation were obtained. The six complexes except that with bridge N_3 ~ - formed dihy-droxo-complexes mainly at about pH 9 and formed monohydroxo-complexes mainly at about pH 7.5.