Small circular DNA molecules with designed lengths, for example 64 and 96 nucleotides (nt), after hybridization with a few 32-nt staple strands respectively, can act as rigid motifs for the construction of DNA nanotubes with excellent uniformity in ring diameter. Unlike most native DNA nanotubes, which consist of longitudinal double helices, nanotubes assembled from circular DNAs are constructed from lateral double helices. Of the five types of DNA nanotubes designed here, four are built by alternating two different rings of the same ring size, while one is composed of all the same 96-nt rings. Nanotubes constructed from the same 96-nt rings are 10-100 times shorter than those constructed from two different 96-nt rings, because there are fewer hinge joints on the rings.