Taylor, a former president of Liberia, was convicted and sentenced to 50 years in prison last year for acts of terrorism, murder, rape and child-soldier recruitment during Sierra Leone's decade-long civil war.
The Special Court of Sierra Leone, which originally sat in Freetown, Sierra Leone, began hearing two days of oral arguments Tuesday at The Hague, Netherlands.
Taylor's lawyers are seeking a reduction or elimination of his sentence while prosecutors were urging the court to impose a harsher punishment, Voice of America reported.
The court convicted Taylor, 64, in April 2012 on 11 counts, saying that even though he did not command and control the rebels who committed the atrocities, he knew of their activities and supplied weapons and other resources to them.
Taylor's attorneys said their client's actions were "done with honor" to bring peace to neighboring Sierra Leone.
Prosecutors have asked the court to impose an 80-year sentence on Taylor, the first former head of state since World War II to be convicted by an international war crimes tribunal.