Shortly after noon at Shoreline Variety, on 334 Lakeshore Road East, the victim left their wallet on a counter momentarily before returning to find it missing.
CCTV cameras captured a 75-year-old woman putting it in her purse.
Halton Regional Police Service (HRPS) are trying to identify the female suspect and determine whether there was criminal intent.
Halton Police would like to hear from you if you have information to share. You can call them by dialling 905-825-4747 or Crime Stoppers at 1-800-222-TIPS (8477).
You can also visit the Crime Stoppers website and leave an anonymous tip.