Abstract: Apparatus for measuring the colloidal stability of liquids comprising a sample-holder containing a sample of the liquid the turbidity of which is to be measured, a cooling tank containing the sample-holder and associated with a cooling unit, a laser light source of appropriate wavelength, a photopile for measuring the light flux diffused through the sample to be checked, a reference photopile for permanently controlling the exciting beam, a semitransparent mirror reflecting a part of the light beam in the direction of the reference photopile, a device for absorbing the nondiffused light and a logic system associated with a microprocessor for calculating the value of the turbidity of the sample.