In order to prepare intermediate for further transformation of penicillins), and to obtain new derivatives with enlarged spectrum of biological activity some semi-synthetic phenoxyalkanepenicillins were subjected to the esterification, amidation and hydroxyamidation reactions. Hydroxyamidation i.e. synthesis of corresponding penicilline-hydroxamic acids was a complex reaction depending on the structure of hydroxylamine used. The two-directional reaction course, with beta-lactam bond splitting, was specific for unsubstituted hydroxylamine only. A number of new penicilline hydroxamic acids and N-methoxypenicilline amides, with intact and cleaved beta-lactam ring were synthesized.