Officers were called out shortly after 5am today and have had the park, next to City Road, sealed off with a police cordon since then.
South Yorkshire Police said of the victim in a statement this afternoon: “A murder investigation has been launched after the body of a man was found this morning (Thursday 12 May) in a Sheffield park.
He is yet to be identified, and officers are working to establish who he is.
“At this time, a police cordon remains at the site. The whole park remains closed off, and people are asked to please avoid the area while officers continue their work. We appreciate your patience while the investigation work continues.
"Anyone with information which could assist with our enquiries, who may have seen or heard any suspicious activity around the park between last night (Wednesday 11 May) and this morning, or who may have CCTV footage which captured any helpful footage, is asked to call 101, quoting incident number 122 of 12 May.
"Alternatively, contact Crimestoppers via their website Crimestoppers-uk.org or 0800 555 111.”
By 7.30am, 11 police cars could be counted along CIty Road, in addition to three police vans, including a scene of crime investigation van. Another police car was parked within the main cordon, in a sealed-off car park.
Police tape extended from the Select and Save supermarket, past the park, and ended just past the York House community building.