The dilute solution properties of lightly sulfonated hydrogenated styrene-butadiene-styrene block copolymer (S-SEBS) dissolved in tetrahydrofunan (THF) were studied by viscometry. The ring conformation in dilute regime can be deduced from the intrinsic viscosity data. It is believed that this special conformation results from the location of ionic group at both two-end blocks. The intermolecular aggregation can be observed when the solutions undergo the freezing-thawing process in the same concentration region. The extent of aggregation is affected by the freezing-thawing cycle times, water content in THF, and the counterion radii, etc. The properties of the aggregation equilibrium are also discussed.