Combinable bottle assembly (1,6) consisting of two separately fillable bottles designed to be fitted together one above the other, can be formed inexpensively of plastic, filled and stored separately from and independently of one another and can readily be connected and tightly combined with one another to form a two-compartment container convertible to a one compartment container.The floor or bottom wall (12) of the upper bottle (1) is formed as a separate cylinder element (3) having an annular connecting plate (13) which connects a skirt wall (14) of the cylinder element to the wall (15) of a central nozzle (9) arranged concentrically therein, forming a throughflow passage (16) which is closed by a stopper (10). The lower bottle (6) comprises an elongate neck having an external screwthread (33) which is engagable with an internal thread on the elongate nozzle to permit the second bottle to be screwed into the nozzle to a connecting position to dislodge the stopper and open the containers to each other.