The inauguration ceremony took place in front of the Georgian parliament's building in the center of Tbilisi on Sunday, with high-ranking officials from around 40 countries attending the event.
"We'll never recognize Saakashvili as our president and will continue our political struggle. The people who have come to the rally have showed to the entire world that Saakashvili is not their president," Giorgy Tsagareishvili, an opposition leader, said.
An estimated 10,000 opposition activists participated in the rally.
On January 13, Georgia's central election commission officially announced Saakashvili as the winner of the early presidential poll in the South Caucasus republic with 53.47% of the vote. His nearest rival, united opposition candidate Levan Gachechiladze, won 25.69%.
However, the Georgian opposition said the election results were rigged and demanded a second round in the January 5 presidential elections. On January 13, when the official election figures were announced, the Georgian opposition held a rally in Tbilisi to protest the vote results.
Saakashvili called the snap elections following mass street protests in Tbilisi in early November fueled by popular discontent with his alleged totalitarian tendencies and the country's economic woes. He ordered a brutal police crackdown on protesters and briefly imposed state of emergency, triggering criticism from his Western allies.
The U.S.-educated president has sought to integrate the ex-Soviet state into Europe and to curb Russian influence on it ever since he came to power on the heels of the peaceful 'rose revolution" in 2003.