Gallic acid (GA) and several gallate derivatives were identified as inhibitors of fucosyltransferase VII (FucT VII). The inhibition by GA and (−)-epigallocatechin gallate (EGCG) is time-dependent and irreversible. GA and EGCG showed inhibition with IC 50 of 60 and 700 nM, respectively, after pre-incubation with FucT VII in the presence of MnCl 2. Absence of MnCl 2 results in significantly weaker inhibition. Complexation of Mn 2+ with GA, EGCG, and gallate esters was observed. Such complexation, however, is not rate-limiting for the inhibition of FucT VII. Therefore, time-dependent inhibition of fucosyltransferases by GA and EGCG is likely due to the slow inactivation by the inhibitors or Mn–inhibitor complex. Although Mg 2+ or Ca 2+ can replace Mn 2+ for FucT VII activation, none forms a complex with GA or EGCG and hence results in weaker inhibition of FucT VII. GA and EGCG also inhibit FucT IV and α2,3-( N)-sialyltransferase in the low micromolar range. The structure–function divergence could be observed, as EGCG, but not GA or gallate esters, inhibits Zn 2+ containing metalloproteases such as TNFα convertase, matrix metalloproteases 2 and 7.