The German has been rewarded for forging a hugely successful partnership with Laurent Koscielny, while the experienced Czech is believed to have committed himself until 2016
Goal reported in October that Mertesacker had opened talks over an extension committing him to the club until 2017 and revealed a new deal for Rosicky was in the offing in November.
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"We are delighted that Mertesacker and Rosicky have committed their futures to the club," Arsene Wenger told the club's official website.
"They are players of exceptional quality and experience, and have consistently proven themselves at the highest level.
"There is a great feeling of togetherness and belief in the group and this news will only help to strengthen this further."
On the announcement of his new deal, Mertesacker said: "It was easy for me to commit myself to the club. I have been here for two and a half great years and feel I have great support from everyone at the club and the fans. I’m really looking forward to having more years coming up with this fantastic club.
"We have a great team here and we all want to do our best to win trophies."
Rosicky added: "Ever since I arrived at Arsenal, I have always felt that I'm at the right place where I want to be. I still feel this way now and I'm proud that after such a long time I'm still here and will continue.
"One big factor is that I want to win the league with Arsenal. It's my big goal and I will do everything that I can to achieve it.
"Arsenal is a great club, we have a great spirit here and we are all working together to do the best we can."