The midfielder is a firm favourite of Blues fans.
"I couldn't have wished for any more in my time at the club so far," Mata tells the official Chelsea website. "Winning both the Champions League and Europa League, and winning the personal trophies for Player of the Year, it's been absolutely amazing.
"It's special because of the fact you spend every day with your team-mates and share all your good and bad moments, so I'm so grateful to all of them for helping me.
"Since I came here everything has been almost perfect for me, the only thing I want now is to keep going and hope the good luck stays with me."