The 49-year-old billionaire heir to South Korea's Samsung Group was convicted by the lower court of bribing the country's former president Park Geun-hye. Besides Lee, who has been in detention since February, four former Samsung executives were also charged in the case.
The lower court had ruled the bribe helped Lee strengthen his control of Samsung Electronics, the crown jewel in the country's biggest conglomerate and one of the world's top technology firms.
"The defendants say they are concerned about the future of Samsung Group. However, what they are really concerned about is Lee's loss of control and subsequent economic losses," special prosecutor Park Young-soo told a packed court of about 150 people.
Lee, in a dark suit and white shirt without a tie at the appeals hearing, earlier on Wednesday denied the bribery charge and also denied recent allegations by prosecutors that he had met Park one-on-one four times, instead of the previously disclosed three times.
The Seoul High Court is expected to rule on the appeal in late January. Whichever side loses could take the case to the Supreme Court, the final court of appeal in South Korea.
The lower court had ruled in August that while Lee never asked for Park's help directly, the fact that a 2015 merger of two Samsung affiliates did help cement Lee's control over Samsung Electronics implied he was asking for the president's help to strengthen his control of the firm.
His lawyers have strongly challenged this logic since appeals hearings began in October.
"The defendants have not once tried to solve issues by colluding with political power and gaining its help. The special prosecution has severely distorted the truth, and that distortion is reflected in the jail term they sought," said Lee In-jae, Lee's lawyer, responding to the 12-year jail term demand.