Glucomannan, a natural polysaccharide extracted from Amorphophallus konjac, was employed as a sieving additive for the separation of restriction DNA fragments in capillary electrophoresis. A stable solution of entangled glucomannan was successfully prepared under mild conditions. The separation capillary filled with 0.25% glucomannan exhibited excellent resolution and reproducibility on separation of DNA fragments over the range of ca. 1400 base pairs. The separation was dependent on the size of the fragments, which allowed the determination of the size of separated DNAs directly from the migration time. In addition to these separation characteristics, glucomannan has practical advantages in its chemical stability, non-toxicity and ease of handling. Because the method is applicable to the separation and characterization of the DNA fragments generated by digestion with restriction enzymes or produced by polymerase chain reactions, it is concluded that glucomannan is a good alternative to the conventional sieving additives for capillary electrophoresis, such as polyacrylamide and hydroxymethylcellulose.