ureido cephalosporin derivatives of the formula ## str1 ## wherein r is hydrogen , lower alkyl , phenyl - lower alkyl , diphenyl - lower alkyl , trisilyl , trihaloethyl , a salt forming ion , or the group ## str2 ## r 1 is hydrogen , lower alkyl , cycloalkyl , cycloalkenyl , cycloalkadienyl , phenyl , phenyl - lower alkyl , substituted phenyl or phenyl - lower alkyl , or certain heterocyclic groups ; r 2 is hydrogen or lower alkyl ; r 3 is hydrogen or methoxy ; r 4 is hydrogen , halogen , lower alkyl , or lower alkoxy ; r 5 is hydrogen or lower alkyl ; r 6 is lower alkyl , phenyl , or phenyl - lower alkyl ; are disclosed . these compounds are useful as anti - bacterial agents .