A molecular dynamics (MD) simulation was carried out for aqueous solutions of cellooligosaccharides to investigate their interactive behavior. Single and double strands of cellotetraose, cellopentaose, and cellohexaose were simulated in systems with TIP3P water. The cellotetraose double strand separated into two within 1 ns calculation time. An aggregation state of a cellohexaose double strand is firmer than that of cellopentaose in the simulation, supporting experimental results. The self-diffusional motion of solutes is approximately in inverse proportion to their molecular surface areas without special interactive effects, while their atomic positional fluctuations manifest the effect of sugar-sugar interaction. Sugar-sugar interaction restrains the fluctuation inversely proportional to the degree of polymerization, as opposed to proportional promotion by sugar-water interaction. The degree of polymerization is at a critical point in cellopentaose, as viewed from the balance between sugar-sugar and sugar-water interaction. The occupancy of intramolecular hydrogen bonds between the particular oxygen atoms, O3 and O5', in adjacent residues is remarkably high in the double strand of cellohexaose among the three cellooligosaccharides, which abundance means a stable state of a twisted ribbon structure of the sugar chain. That leads to a higher occurrence of intermolecular hydrogen bonds between sugar chains using the oxygen atom O6 in cellohexaose than in cellotetraose or cellopentaose.