FIELD: biotechnology, microbiology. SUBSTANCE: invention relates to method of preparing and/or purification of clavulanic acid or its pharmaceutically acceptable salt or ester. Method involves removal of solid substances from fermentation broth containing clavulanic acid by microfiltration to form the first filtrate with pH 5.8-6.2 followed by removal of solid substances from the first filtrate by ultrafiltration using polysulfone membrane providing removal of substances with molecular mass from 10 to 30 kDa with passage capacity from 10 to 30 l•m-2•h-1. Formed second filtrate is concentrated by water removal and obtained concentrated second filtrate is treated to yield clavulanic acid or its pharmaceutically acceptable salt or ester. Method provides decrease the content of impurities showing absorption at 420 nm. EFFECT: enhanced effectiveness of isolation and bleaching of clavulanic acid. 7 cl, 1 ex
