The present invention relates to an antibody comprising a GlcNAc-S(A)x substituent, wherein S(A)x is a sugar derivative comprising x functional groups A wherein A is independently selected from the group consisting of an azido group, a keto group and an alkynyl group and x is 1, 2, 3 or 4, wherein said GlcNAc-S(A)x substituent is bonded to the antibody via CI of the N-acetylglucosamine of said GlcNAc-S(A)x substituent, and wherein said N-acetylglucosamine is optionally fucosylated. The invention also relates to an antibody-conjugate, in particular to an antibody-conjugate according to the Formula (20) or (20b), wherein AB is an antibody, S is a sugar or a sugar derivative, D is a molecule of interest, and wherein said N-acetylglucosamine is optionally fucosylated (b is 0 or 1). The invention further relates to a process for the preparation of a modified antibody, to a process for the preparation of an antibody-conjugate, and to said antibody-conjugate for use as a medicament. In addition, the invention relates to a kit of parts comprising an azide-modified antibody and a linker-conjugate, wherein said linker-conjugate comprises a (hetero)cycloalkynyl group and one or more molecules of interest.