Ajax signed former Germany international Heiko Westermann from Real Betis to a two-year deal on Saturday.
The centre-back moves to the Dutch giants on a free transfer despite having a year left on his contract in Spain.
"I am very happy with my contract at Ajax," the 32-year-old told the club's official website.
"We had a great chat last week and I immediately knew that I wanted to join Ajax. It's fantastic that it's all gone this quick.
"Ajax are a great club with a world-famous philosophy. It's a young team with a lot of big talents. I hope to be able to help them with all my experience, having played in the Bundesliga and in Spain.
"I want to win the Eredivisie title here."
Westermann, who said in January that he would like to play in the United States, only spent one year in Spain with Betis, scoring once.
