"It has been a truly amazing year for me," said Jankovic. "Winning four Sony Ericsson WTA Tour titles, over 60 matches and to make it to two semi-finals and a final in the Grand Slams of 2008 is a dream come true.
"I worked really hard this year and to finish number one is where I want to be and where I hope to stay."
The Serbian holds 4,555 points, a commanding lead over Dinara Safina (3,782) and Serena Williams (3716).
The 23-year old secured the number one spot by winning 12-straight matches en route to three consecutive titles - the China Open in Beijing, the Porsche Tennis Grand Prix in Stuttgart and the Kremlin Cup in Moscow.
Those successes took her title count for the year to four as she had already claimed the Internazionali BNL d'Italia in Rome.
Jankovic also reached the final of the US Open and the semi-finals of the Australian and French Opens.