The present invention provides a method for measuring a cellular uptake amount of a molecule, comprising (i) adding the molecule to an organ-derived cell population to perform incubation, (ii) sorting the organ-derived cell population based on the expression levels of CD31 and CD45, and (iii) after steps (i) and (ii), measuring the amount of the molecule incorporated into the cell population sorted in the step (ii), wherein the molecule is incorporated into cells via a cell surface receptor.