The present invention provides a novel glycopeptide antibiotic derivative.These derivatives are represented by the formula (I) or a pharmaceutically acceptable salt or solvate thereof, wherein RA is —X1—Ar1—X2—Y—X3—Ar2 wherein X1, X2 and X3 are single bond; heteroatom-containing group selected from the group consisting of —N═, ═N—, —NR1— (R1 is hydrogen or lower alkyl), —O—, —S—, —SO— and —SO2—, or a linkage thereof; or alkylene or alkenylene optionally substituted and optionally interrupted by one or more of said heteroatom-containing group; Y is —NR2CO—, —CONR2— (R2 is hydrogen or lower alkyl), or a group of the formula (II) wherein R3 is alkylene; Ar1 and Ar2 are a carbocycle or a heterocycle which is optionally substituted and may have an unsaturated bond; RB is —NHNRXRY or —NRZORW wherein RX is hydrogen or lower alkyl; RY is hydrogen, optionally substituted lower alkyl, C(═NH)NH2, CSNH2, COCONH2, CN, optionally substituted heterocyclic group, and optionally substituted carbamoyl; RZ is hydrogen or lower alkyl; RW is hydrogen, optionally substituted lower alkyl, optionally substituted lower alkenyl, optionally substituted heterocyclic group, optionally substituted heterocyclic carbonyl or optionally substituted carbamoyl; RC is hydrogen or optionally substituted alkyl, wherein said alkyl may be interrupted by a heteroatom-containing group selected from N═, ═N—, —NR1— (R1 is hydrogen or lower alkyl), —O—, —S—, —SO— and —SO2—; and R is optionally substituted alkyl.