The 34-year-old has called time on his Test career on the back of the Springboks' Rugby World Cup triumph in Japan.
Louw played 76 times for the world champions and Rugby Championship holders after making his debut against Wales in 2010.
South Africa director of rugby Erasmus paid tribute to the forward, who will continue to play for Premiership side Bath.
Goodbye to a warrior of 76 Tests
Test tries and numerous turnovers
Thank you for the memories 'Flo'
— Springboks (@Springboks) November 10, 2019
Erasmus said: "Flo was a real warrior of the back row.
"He was always ready to go where the fire was hottest and was the kind of tough-minded character that you'd always want beside you. He didn't take a step backwards ever.
"He has been a tremendous servant of South African rugby and we're losing a lot with his retirement, not just in how he played, but in the calmness, insight and character that he brought to the group."
Louw said: "I've had an amazing journey in international rugby.
"I've made friends for life in the game and created incredible memories with great people."
Photo Getty Images Caption: World Cup-winning back-row Francois Louw