The versatile defender, who played 100 times for his country over a period of 12 years, made the announcement on Tuesday on the website of his new club Monaco.
"I will no longer wear the jersey of the national team," he said.
"I am proud of everything I have accomplished with Croatia and I am proud of each of my 100 caps.
"I wish to thank all the Croatia supporters and all the people who have helped me over these years."
Simic made his debut for Croatia at the age of 20, in a friendly match against Israel in March 1996.
He was part of the squad that reached the semi-finals of the 1998 World Cup in France and was also a quarter-finalist with his country at Euro 2008.
He won his 100th cap in a friendly clash against Slovenia in Maribor last month.
The 32-year-old, who has played for Dinamo Zagreb, Internazionale and AC Milan in a distinguished playing career, scored three goals for Croatia.