Provided is a resin composition, comprising: an isobutylene-based copolymer (A) containing a halogen atom； an ethylene-vinyl alcohol copolymer (B)； and a halogen scavenger (C), wherein a mass ratio (B/A) of the ethylene-vinyl alcohol copolymer (B) to the isobutylene-based copolymer (A) containing a halogen atom is from 20/80 to 50/50, and a content of the halogen scavenger (C) is from 0.01 to 1 part by mass based on 100 parts by mass of a total of the isobutylene-based copolymer (A) containing a halogen atom and the ethylene-vinyl alcohol copolymer (B). Such a resin composition is excellent in gas barrier properties and flexibility and stably produced over a long period of time.
