3'-O-Stearoylation of 6-azauridine was achieved enzymatically for the first time. Among eight commercially available lipases, that from Burkholderia cepacia displayed a 3'-regioselectivity of 80% towards the acylation of 3-hydroxyl of 6-azauridine. Using an immobilized lipase from Burkholderia cepacia, the 3'-regioselectivities of the acylations could be reversed by lengthening the aliphatic chain of the acyl donors (C2-C18). The possible reason might be the presence of the interaction between the base moiety and the acyl group.