The molecular weight distribution by sedimentation velocity measurements and hydro-static pressure correction for the sedimentation coefficient of the floating system poly-dimethylsiloxane—bromocyclohexane at θ-temperature (28℃) have been studied．A new method for the experimental evaluation of the hydrostatic pressure correction of the sedi-mentation coefficient is proposed．By using different quantities of the solution added to the sedimentation cell，so as to give different heights of the liquid column，it is possible to determine the influence of the hydrostatic pressure on the sedimentation coefficient．Assuming a linear relation between the sedimentation coefficient and the hydrostatic pressure

the authors found that the pressure coefficient of the system studied is 1．44×10-3 (atm)-1 for hydrostatic pressures less than 200 atm．From the distribution of sedimentation coefficients，and the values of Mw [n]θ，and [n]toluene of a polydimethylsiloxane fraction the monodisperse relationships s-M，[n]θ-M，in the θ-solvent at 28℃ and [n]toluene 一M at 25℃ are obtained.