I don't know if it has an expiry date or not, but since it's inexpensive, I'd suggest buying some new salts to ingest.

Use the old salts in a bath. This helps to draw out toxins (and you can use it to exfoliate), so this would be a good thing to do during a cleanse anyway!

If you want more info about Epsom Salts in baths (or its many other uses), I found a webpage:

http://www.epsomsaltcouncil.org/index.cgi

From the site:
{{" Epsom Salt baths are an excellent way of combating stress and alleviating muscular aches and pains. The high magnesium content in Epsom Salt baths facilitates the removal of acids through the skin. They are, therefore, a wonderful natural treatment for sportsmen and women as well as patients suffering from Arthritis and rheumatism."
Internet Health Library }}

Elaine

I can't imagine salt expires, but I would certainly be concerned about possible dust accumulation over the years it has been sitting in the carton.