It should be stamped Tiffany & Co. 925 on the inside, however, a good knockoff will also have this stamp. My suggestion would be to take it to Tiffany's (if you have one nearby) do not tell them that it was bought over the internet or they probally wont even look at it, just say it was a gift. You could also take the bracelet to a reputable jewlery repair shop or collector (don't use a jewlery shop at the mall like Kay or Jerrod's, they wount have a clue). Hope this helps.