PROBLEM TO BE SOLVED : To provide an autonomous sink-and-float material which does not require a condition of weak acid, can be used over a wide range of aqueous media, and can repeatedly sink and float, and a method for autonomous sink-and-float of a molding using the material in the aqueous medium.SOLUTION : The invention relates to a composition used for autonomous sink-and-float in an aqueous medium, the composition comprising, in a matrix of a matrix formation material : a microbe and/or minute organism forming gas and/or aqueous medium insoluble liquid by an organism activity; and a substance for creating gas and/or aqueous medium insoluble liquid by utilization of the microbe and/or minute organism. The molding formed of the composition is added to the aqueous medium, for autonomous sink-and-float of the molding in the aqueous medium (specific gravity of the molding is larger than that of the aqueous medium).SELECTED DRAWING : None