The present invention is related to a reagent vessel, comprising: at least one first tube and at least one second tube, wherein second tube has a section area of the opening greater than one of the bottom. A kit for a reagent vessel is also provided herein, comprising: the reagent vessel and a stirrer jacket, wherein the section area ratio value for the bottom of the second tube to the stirrer jacket is 1.1 to 3.5. According to the present invention, an optimum efficiency for the stirrer jacket will be achieved, and a high capacity of the operational volume will be maintained thereby.