The pope "rested well during the night. His clinical picture is gradually improving and he is continuing his planned treatment", spokesman Matteo Bruni said in a statement.
"This morning after breakfast, he read some newspapers and resumed work. Before lunch, he went to the little chapel of the private (hospital) apartment where he prayed and he received the Eucharist."
Pope Francis, who earlier this month marked 10 years as head of the Catholic Church, was admitted to the hospital on Wednesday, for what the Vatican initially said were pre-planned tests, forced him to cancel a number of engagements.
It also raises questions over his presence at services for the upcoming Holy Week and Easter, Christianity's most important holiday.
The Vatican late Wednesday said the pope had a respiratory infection that would require hospital treatment for "a few days", adding that Covid had been excluded.
Over the past year Francis has suffered from chronic knee pain that has required him to use a wheelchair.
His postponement last year of a scheduled trip to Africa and various events at home fueled intense speculation about his health, and in a July 2022 interview he acknowledged he needed to slow down.
At his weekly audience at the Vatican on Wednesday morning, just hours before his admission to hospital, the pope appeared in good spirits, smiling as he greeted the faithful from his "popemobile".
But he was pictured wincing as he was helped getting onto the vehicle - a photo that made all the major front pages of Italy's newspapers on Thursday.
Francis was admitted in July 2021 to the same Rome hospital for 10 days for an operation on his colon after suffering from a type of diverticulitis, an inflammation of pockets that develop in the lining of the intestine.
In an interview in January, Francis said the diverticulitis had returned.
Francis has repeatedly said, most recently in February, that he would consider stepping down if his health required, following the example of his predecessor Benedict XVI.
He has cautioned, however, that papal resignations should not be the norm, and said in an interview last month that the idea was currently not "on my agenda".
Despite his health issues and advancing age, Francis - a Jesuit who seems most happy being among his flock - continues to travel internationally.
Earlier this year, he visited South Sudan and the Democratic Republic of Congo, drawing huge crowds.
Next month, he is due to visit Hungary and meet Prime Minister Viktor Orban.
Pope Francis 'Improving': Vatican
update
UPDATED WITH ADDITION INFORMATION ON CONDITION: ROME - Pope Francis's health is improving after spending a night in hospital with a respiratory infection, the Vatican announced Thursday, saying the 86-year-old had eaten breakfast, read the newspapers and even done some work.
