"I have played many matches against Djurgården and I know how tough it is to be on the other side.
It's a strong team with a winning mentality, so when I was asked the question, I didn't feel like I needed to think too much," he says to Djurgården's website.
Gracia played 28 Allsvenskan matches for Mjällby this year and scored four goals.
The Spaniard has previously also represented Gif Sundsvall.
Gracia's contract with Mjällby expires at the turn of the year and he joins Djurgården on a free transfer.