The results of viscometric and optical microscopic studies indicated that both Syntan 25 and Syntan PUR in aqueous concentrated solutions (above their c.m.c. values) at 25 °C are spherical in shape. The size and other physico-chemical parameters e. g. Volumes of the aggregated particleMv, Radius of gyrationRg, Hydrodynamic radius ¯Rh, Diffusion coefficient ¯D, and the Correlation times for aggregate rotationTr Translational diffusionTD and effective aggregation timeTa have been derived on the basis of microscopic results. The viscosity data for both Syntan 25 and Syntan PUR were analysed in terms of Einstein equation, Moulik equation, Jones-Dole equation. It has been shown that Syntan PUR was more highly hydrated than that of Syntan 25 although the intrinsic viscosity [η], of Syntan PUR is nearly 1.5 times greater than that of Syntan 25. The Flory-Huggins equation and Thomas equation has been compared in both the Syntans and it has been concluded that the Thomas' constantk1 may be 12.50 for perfect spherical shape of the particle instead of 10.05 (which has originally been proposed by Thomas).