Hydroxy propyl cellulose(HPC)is a non—ionic water soluble polymer which has a characteristic cloud point at or above which the solution becomes turbid．The cloud point has most commonly been measured by recording the temperature at which the solution becomes turbid and occasionally using light scattering techniques or turbidity measurements．Since Cloud point also iS congruent with the onset of separation ofpolymer rich and polymer depleted phases．It iS expected that there will be an abrupt change in the flow behaviour of the polymer solution before and after the cloud point．We have．Therefore．Investigated the clouding ofpolymer Solution from the changes in the viscosity of aqueous Solution of HPC as a function of temperature．Viscosity of the polymer solutions were measured using a SV-1 0 Vibro viscometer (A&D． Company Limited．Japan)equipped with two thin sensor plates immersed into the measuring sample in the measuring vessel．The Vibro—Viscometer has a wide dynamic range of viscosity from 0．3mPa．S to 1 0．000mPa．S with maximum uncertainty Of 1ess than 0．1％．The wide dynamic range enables to measure viscosity changes continuously even after the clouding of the solution．It was found that there iS a sharp decrease in the viscosity of the polymer solution at the cloud point temperature and hence．The cloud point of the polymer solution may be precisely measured from viscosity measurements．The cloud point determined from viscosity measurements agreed very well with the ones measured by spectrophotemric or direct visual techniques．The ef’fect of added electrolytes．Anionic or cationic surfactants on the cloud point ofHPC would be discussed in the presentation．