Bolsonaro said he started feeling unwell on Sunday afternoon after lunch and doctors have inserted a nasogastric tube.
Medical officials on Monday described his condition as stable and improving.
"More tests will be conducted for a potential surgery on an internal obstruction in the abdominal region," Bolsonaro posted on Twitter, along with a photo of himself giving a thumbs-up in his hospital bed.
Bolsonaro said it was the second hospitalisation "with the same symptoms" since he was stabbed during a September 2018 campaign event and underwent a series of emergency operations.
Vila Nova Star hospital in Sao Paulo confirmed the president was admitted to the hospital in the early hours of Monday local time with an intestinal blockage.
"He is in stable condition, undergoing treatment," it said.
"At the moment, there is no forecast for him being discharged."
In a separate statement in the evening, Vila Nova Star said Bolsonaro was improving and had taken a brief walk in a hallway.
The hospital said he was not suffering from fever-like symptoms or abdominal pain, but it was not yet clear if he would need surgery.
TV network Globo showed images of Bolsonaro, who had been holidaying in the southern state of Santa Catarina, walking down the stairs of the presidential plane after landing in Sao Paulo around 1.30am local time.
In July 2021, he was taken to the Vila Nova Star hospital in Sao Paulo due to an intestinal blockage after suffering from chronic hiccups
The far-right Bolsonaro has been in power since 2019 and plans to stand for re-election as president in a vote scheduled for October this year.
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