The 66-year-old veteran politician, who was acquitted in 2012, slammed the appeal, saying it was a political ploy to tarnish his image in the conservative Muslim-majority nation.
"There is absolutely no case for them. This is clearly seen to be political," Anwar said as he entered the Court of Appeal with his family for the hearing in the administrative capital of Putrajaya.
Anwar will contest a seat in central Selangor state, the country's main economic hub surrounding the capital Kuala Lumpur, in a by-election set for March 23.
The sodomy appeal hearing has been postponed numerous times as the defence has sought but failed to disqualify the government's lawyer, alleging he is biased toward the long-ruling coalition.
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A Kuala Lumpur high court had previously found Anwar not guilty of having sex with a young, male, former aide following an acrimonious two-year trial.
In his ruling, the judge said controversial DNA evidence submitted by the prosecution in the case was unreliable.
Anwar has dismissed the charges as a political ploy to send him to jail and damage his reputation after key opposition gains in 2008 elections.
Sodomy is illegal in Malaysia and punishable by up to 20 years in jail.
It is not the first time the former deputy premier has faced sodomy charges.
In 1998, he was sacked from the number two post by then-ruling strongman Mahathir Mohamad and jailed on sodomy and corruption charges.