The sentencing of the billionaire scion was a watershed for South Korea's decades-long economic order, which has been dominated by powerful, family-run conglomerates.
Lee's lawyer has steered media inquiries to Samsung, whose spokeswoman did not have any immediate comment about the appeal against the sentence handed down on Friday.
Lee, the 49-year-old heir to one of the world's biggest corporate empires, was detained in February on charges that he bribed then-president Park Geun-hye to help him secure control of the conglomerate that owns Samsung Electronics, the world's leading smartphone and chip maker.
Samsung Group also has interests ranging from drugs and home appliances to insurance and hotels.
Under Korean law, Lee can be kept in detention a maximum four months while a court considers his appeal. This means the appeals court that is assigned the case is likely to try to wrap up its ruling around January 2018, said criminal lawyers not directly involved in the case.
Samsung Electronics Chief Executive Kwon Oh-hyun asked employees to rally around the company.
"I believe all of you must be devastated by the lower court ruling... We management are also distressed," he wrote in an internal message, seen by Reuters, to Samsung Electronics staff on Monday.
"Please do the best you can where you are... We management will also lead the way in overcoming the crisis with uncommon resolve," Kwon added.