A novel hydrophobic colorimetric film was developed using ethyl cellulose (EC), castor oil (CO) and purple potato anthocyanin (AN) for pork freshness monitoring. The films with CO concentrations of 0% (control), 0.25%, 0.5%, 1% and 2% were developed and expressed as F0, F0.25, F0.5, F1 and F2. Scanning electron microscopy (SEM) images showed that the five films had dense surface and porous internal structures. The F0.5 film exhibited the highest tensile strength (TS) value, optimal color stability, ability to prevent the leaching of AN. The limit of detection (LOD) value of the F0.5 film to ammonia gas was 1.04 μM. The color of F0.5 film turned from red to green along with the spoilage of pork. As a result, the film was expected to be a good colorimetric indicator of pork freshness for intelligent packaging.