A method for manufacturing a lithium ion polymer battery is provided in which in injecting electrolyte into a lithium ion polymer battery, the battery cell is immersed in an electrolyte impregnation bath to allow the electrolyte to be impregnated into the cell. The electrolyte can be impregnated simultaneously, and as the battery cell is activated, the electrolyte is settled down in the interior of the battery cell. Thus, when the battery cell is sealed, a phenomenon that the electrolyte is present at the sealed portion can be prevented.