The Proteas, who had topped the rankings since displacing England in August 2012, slipped below Australia after the results from the 2010-11 season were dropped from the calculations.
The Australians have also retained their top ranking in one-day internationals ahead of India, who have fallen from third to fifth in the test rankings behind the top two nations as well as England and Pakistan.
"We are incredibly proud to be the number-one ranked team in the world in both test and ODI cricket, which are two of the team's most important goals," said Australia captain Michael Clarke.
"There has been an enormous amount of hard work and effort on and off the field that has led to this result.
"However, the true test of a great side is sustained success and now our goal is to maintain these rankings and continue to play great cricket as we lead into challenging test series against Pakistan and India, and the ICC Cricket World Cup at home."
Australia topped the rankings from their inauguration in 2003 to 2009 before being displaced briefly by South Africa, with India (2009-2011) and England (2011-2012) then ruling the roost.
(Reporting by Nick Mulvenney, editing by Peter Rutherford)
