Provided is a container for preparing a diluted solution of a biological sample to be used for biological sample analysis. Specifically, provided is a container for specimen dilution, including: an open; a first bottom; a second bottom formed on an inner side wall of the container; and a groove upwardly formed, on the inner side wall of the container, from the second bottom, in which the groove has a constant width equal to a width of the second bottom, or the groove has, at a lower end thereof, a width equal to the width of the second bottom and upwardly widens.