His trial began at the Kuala Lumpur High Court earlier this month with testimony from his accuser, who claimed Anwar had "side B-sex" with him in 2008.
Anwar says the charges are part of a "political conspiracy" and that they are "malicious" fabrications.
"It is a malicious charge. It is a frivolous charge. It is trumped up by political masters using the prosecution for that purpose," he said recently.
Prosecutors have promised to produce semen samples that they said were found in medical tests on Mohamad Saiful Bukhari Azlan, the male aide who made the allegations.
"The prosecution will then prove [guilt] beyond reasonable doubt through the testimony of Mohamad Saiful Bukhari Azlan and forensic evidence from doctors and chemists alongside circumstantial evidence and documentary evidence," Mohamed Yusof Zainal Abiden, the deputy public prosecutor, said.
Sodomy, even among consenting adults, carries a penalty of up to 20 years in Malaysia.
The trial began after months of delays caused by defence applications to strike down the case and obtain access to evidence, including medical reports and closed-circuit television footage, denied them by a higher court ruling.
The case has placed the Malaysian judiciary under scrutiny again after Anwar's conviction for the same offence almost a decade ago was eventually overturned.