Lee, 72, is credited with turning the once-obscure South Korean company into the electronics giant currently leading the world's memory chip and smartphone markets.
His failing health has fanned concerns over potential disruption in Samsung's management, with company officials largely tight-lipped over details of his condition.
"He is recovering steadily and gradually," Samsung group spokesman Lee June told reporters, without elaborating.
It is not known when Lee will be able to leave hospital but a lift was recently installed at his Seoul home to "prepare for various possibilities including his release from hospital", the spokesman said.
Recent health problems have led Lee to become less involved in the day-to-day running of the business empire, founded by his late father in the 1930s.
But Lee still has a major say in important strategic decisions, as the group steps up efforts to pave the way for his son, Jay Y. Lee, to take the helm.
The junior Lee is currently the vice chairman of Samsung Electronics, which accounts for the lion's share of the group's sales and profits.
The Lee family controls the vast group, whose businesses range from construction to fashion, through a highly complex web of cross shareholdings across its subsidiaries.
Samsung however has faced growing challenges as its flagship electronics unit is hit by slowing demand and increased competition in the key smartphone sector.
The firm on Tuesday flagged a near 60 percent on-year drop in its third quarter operating profit, following a 25-percent drop in the second quarter.
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