Abstract: A weather strip 20 for double doors comprises: an installation base member 21 installed on a door join part side of a prior dosing rear door 2 of double doors arranged on a side part of an automobile; a hollow seal member 22 which is integrally molded with the installation base member 21 and makes an elastic contact with a post closing front door 1 when the door is closed; and a fin 50 connected to a lower side of the hollow seal member 22, which includes a plane installation piece 51 installed on a lower end on a door join part side of the rear door 2 and a seal piece 52 which is integrally molded with the installation piece 51 and makes an elastic contact with the front door 1 when the door is closed, wherein: the installation piece 51 of the fin 50 has a concave ditch 80 formed on an installation surface side thereof, continuously extending from a lower side of the hollow seal member 22 to a hole 130 which is provided on a lower end on the door join part side of the rear door 2 and bores in the rear door 2