The synthesis of 3-substituted l-fuco-azafagomines from d-lyxose is reported. They represent the first example of aza-C-glycosides having a biimino (-NH-NH-) moiety. The key step of the synthesis is the introduction of the hydrazine moiety by reductive hydrazination of a 1-deoxy-ketohexose with tert-butyl carbazate. Their glycosidase inhibitory properties are also reported.