This study proposes a stretchable photonic crystal (PC) film for visible detection of spoilage milk. Thermoplastic polyurethane (TPU) was used as the substrate for the PC structure. The back-barrier layer of an AAO film was used as the template to form a nickel mold through electroforming. The back-barrier array was then transferred onto the TPU substrate through nanoimprinting. Experimental results confirmed that that the structural color change of the fabricated PC TPU film can be easily achieved by a relatively small stretch force. Further experiments on spoiled milk detection demonstrated that the proposed PC TPU film is a highly smart and cost-effective biosensor for the detection of spoiled foods in a container.