Novel antibiotics derivatives 7-(5-acylamido-5-carboxyvaleramido)-3-(.alpha.-methoxy-p-acyloxycinnamoyloxymethyl)-7-methoxy-3-cephem-4-carboxylic acids and the salts thereof which are useful as antibiotics and intermediates for the preparation of cephamycin derivatives, a process for preparing the same, and a process for recovering the cephamycin derivatives effectively and stably from the fermentation broth in the form of an N-acyl derivative.