The technique of intensity photon correlation spectroscopy has been utilised to investigate the native conformation of lysozyme in water/ethanol mixture as a function of alcohol concentration in the water-rich region of composition (cosolvent mole fraction x(2) < 0.08). A non-trivial behaviour of the hydrodynamic radius is obtained, characterised by a minimum at x(2) = 0.02 and a maximum at x(2) = 0.06. This behaviour is similar to that of partial molar volume of ethanol in water and reflects changes in the alcohol/water structure. The results are discussed in connection to the effect of alcohol in modulating solvent-mediated interactions.