Neighbors said they had not seen the man in more than a week, and had opened a window to provide food and water for the barking dog.
A maintenance worker entered the apartment Saturday and discovered the body, the Wichita Eagle reported Tuesday.
"The dog had been feeding on the man's body," police Lt. Doug Nolte said Monday.
Because his body was partially eaten away, it was not possible to readily identify him, Nolte said.
The dog, described as a pug mix, was held by Wichita Animal Control.