A process for preparing a laminated retort container for packaging foodstuffs which container withstands without delamination food retort conditions up to a temperature of about 140.degree. C. and foods having a hgih acidity, oil, flavoring agents or spices content, said process comprising laminating an aluminum substrate to at least one polyolefin film selected from the group consisting of high-density polyethylene, polypropylene, ethylene-polypropylene copolymers and polybutene films using as an adhesive a specific polyolefin resin in melted state prepared by incorporating aluminum hydroxide with copolymerized (A) and (B), where (A) is at least one member selected from the polyolefin resin group consisting of high-density polyethylene, polypropylene, ethylene-propylene copolymers and polybutene, and (B) is maleic anhydride, and by rendering the so-modified polyolefin resin substantially free from unreacted maleic anhydride and low molecular weight maleic anhydride homopolymers.