The attack happened at around 3.30pm on Tuesday afternoon in the chic 6th arrondissement.
The man threatened the owner and one of her employees with the gun before helping himself to jewellery in the shop's window.
He didn't count on the owner seizing a teargas canister and using it against him.
After spraying him with the gas, she then struggled with him while the employee alerted police.
Police arrived and caught the robber who is now being held for questioning.
The brave shop owner was taken to hospital with some injuries to her back.