Abstract: A process for preparing a well crystallized alkali metal salt of 3, 7-substituted 7-aminocephalosporanic acid derivatives having the general formula: ##STR1## wherein: R1= ##STR2## R.sup.2 =CH3 or C1 M=Na or Kfrom the acid-form derivatives. The process includes preparing a 30% suspension by weight of the acid-form derivative in concentrate alcohol containing 3 to 7% of water by weight, and add an alcoholic solution of alkali base to the suspension under room temperature. The alcohol used to dissolve the base also contains 3 to 7% of water. After a reaction time of 5 to 20 minutes, cool the mixture and let the salt crystallize, and separate the latter from the liquid phase.