Anwar is expected to win the vote and gain a seat in parliament on the back of promises to bring about change and forge national unity.
Anwar has repeatedly threatened to overthrow the BN government led by Abdullah Ahmad Badawi, the Malaysian prime minister, through defections of ruling coalition MPs.
Anwar's aides claim up to 30 of them are willing to defect if he wins the by-election.
Last month, the new sex allegation surfaced as Anwar stepped up his campaign to return to parliament.
He claims the BN "orchestrated the entire malicious, dirty campaign in time for this election", referring to the sodomy charge filed by Mohamad Saiful Bukhari Azlan, 23, a former aide.
Under Malaysian law, sodomy is illegal even if consensual and a conviction could see Anwar jailed for up to 20 years.
Election law rules that a person can contest an election unless he or she is convicted of an offence before polling day.
"What is important to me is to win, whether it is by a margin of one or 10,000, it doesn't matter," Anwar said on Monday.
Anwar, who was deputy prime minister before he was sacked on sodomy and corruption charges 10 years ago, is expected to secure most of the ethnic Chinese and Indian votes.
Ethnic Malay voters, however, appear split between him and the BN's Arif Shah.
Ibrahim Suffian, director of the independent Merdeka Centre, which conducted a telephone poll of 544 voters from Friday to Sunday, said more than half believed that Anwar was "capable of bringing change that will benefit the people regardless of race".
"I think it's a test of who protects the Malay interests the most, to which party will they entrust the political future."