"His arms, legs and feet regain more strength and he can stand without a walker for support for some time. He can exercise for a longer time," said the Royal Household Bureau statement issued late Monday.
Bhumibol was admitted on Oct. 13 to Siriraj Hospital in Bangkok, where he remains. His physical strength has gradually increased, and doctors said his inflamed large intestine returned to normal and they stopped giving him antibiotics.
Bhumibol, the world's longest-serving living monarch, is a unifying figure in Thailand, which usually turns to him in times of crisis, even though his powers are limited as a constitutional monarch.
Bhumibol has suffered from several ailments including heart problems in recent years. He celebrated his 60th year on the throne with lavish festivities last year.
The king is scheduled to preside over a royal barge procession on Nov. 5 , an event organized to mark the end of the three-month Lent period in Buddhist tradition.
The bureau also said the condition of Princess Galyani Vadhana, an 84-year-old sister of the king who was admitted to the same hospital, had also improved. She was hospitalized on June 15 after doctors found abdominal cancer.
More than 500,000 well-wishers have signed a book at the hospital to offer their best wishes to the king and princess.