In situ transmission selctron microscopy is used to study dissolution of liquid single-phase Pb/Bi inclusions attached to grain boundary in an alloy of Al_99.29Pb_0.65Bi_0.06 at temperatures of 343, 370, and 389 °C, respectively.  The initial size of the inclusions was smaller than 60 nm.  Dissolution of the inclusions was observed until their complete disappearance. Digitized video recordings of the process of dissolution were used to obtain the dependence of the inclusion size with time. The kinetics of the dissolution of the grain boundary inclusions can be described with a model where it is assumed that grain-boundary diffusion of Pb and Bi is the controlling mechanism. The high value (2.3 eV) of the apparent activation enthalpy of dissolution indicates that the process is likely governed by the large negative enthalpies of solubility of Pb and Bi in Al.