An object of the present invention is, in the case when a specific substance that has expressed on cells to be detected in a liquid sample is to be specifically stained, to provide a convenient cell staining method by which the damage and loss (flow out) of the cells in the collected sample are prevented, and the time has been shortened in a procedure for staining the cells in the liquid sample. Furthermore, another object of the present invention is to provide a sample collection tube that is suitable for use in the above-mentioned cell staining method. A method for specifically staining a specific substance possessed by cells in a sample, including performing the following steps in one step: (A) a step of performing an immobilization treatment of the cells; and (B) a step of performing a permeabilization treatment of the cells.