A method for reinforcing a weak sealed portion of a multi-chamber medical container by simple processing. The method for reinforcing a weak sealed portion of a multi-chamber medical container includes a multi-chamber container forming step for forming a multi-chamber medical container 10 including a first container portion 11 for containing a medicine, a second container portion 12 for containing a medical solution, an empty container portion 13, a pair of lateral side strong sealed portions 16 for forming both side ends of the container portions, a medical solution side weak sealed portion 17 for forming a partition between the first container portion 11 and the second container portion 12, and a discharge side weak sealed portion 18 for forming a partition between the first container portion 11 and the empty container portion 13; and a weak sealed portion reinforcing step for bonding a reinforcement film 20 for reinforcing the discharge side weak sealed portion 18 so as to cover the surface of the first container portion 11 and so as to be spaced in the discharge direction 14 from a first border 19 with the first container portion 11 on the discharge side weak sealed portion 18.