Abstract: A method for producing a floating body such as a balloon and the like which has a first swelling portion with a gas inlet port and a plurality of second swelling portions each communicating with the first swelling portion, comprising the steps of:folding a single multi-layer film having a sealing capability and pleat portions so that the nonpleat portion, correspond to the first swelling portion of the floating body is formed in the film and pleat portions corresponding to the plurality of second swelling portions;sealing the folded multi-layer film along a seal line which extends over both the pleat and nonpleat portions and forms the gas inlet port in the nonpleat portion to produce the first swelling portion and the plurality of second swelling portions; and cutting and removing material located externally of the sealed multi-layer film along a line substantially parallel to the seal line.