The present invention relates to a multi-chamber medical bag, which is capable of obtaining a positive mixture of medicines, prior to the discharge thereof. A weak seal 24 is provided for dividing the space inside the medical bag 10 into the left-handed and right-handed partitions 26-1 and 26-2. The weak seal 24 has a first portion 24-1 extending between the partitions 26-1 and 26-2 and a bifurcated adjacent to and faced with an outlet port 12. Additional strong seals 30-1 and 30-2 are arranged on both sides of the second portion 24-2 and extend at right angle to the first portion 241 toward the strong seal 14 at the outer periphery of the medical bag. When the partition 26-1 or 26-2 is pressed, the resultant inflated deformation of the medical bag is mainly directed to the first portion 24-1 due to the existence of the additional strong seals 30-1 and 30-2, which allows the last portion to be separated, resulting in a mixing of the medicines in the partitions 26-1 and 26-2. The second portion 24-2 is the opened, which allows the mixed medicines to be introduced into the outlet port 12.