The Milan club sit ninth in Serie A having won just four of their opening 11 league matches.
Inter president Erick Thohir previously gave his backing to Mazzarri, but a 2-2 draw at home to Verona last Sunday proved to be his final game in charge.
A short statement released on Inter's official website on Friday read: "FC Internazionale announces that Walter Mazzarri has been relieved of his duties as first-team coach.
"The club would like to thank Mazzarri for the commitment, dedication and professionalism he showed over his 17 months in charge.
"Today's training session will be taken by Giuseppe Baresi."
Reports in Italy suggest Roberto Mancini will return for a second stint as Inter boss.
During his first reign in charge, Mancini led Inter to three straight Serie A titles between 2006 and 2008, while he also won the Coppa Italia twice.
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