The American man was stabbed in the back by a 61-year-old Chinese man in Qianmen, located just south of Tian'anmen Square, the Beijing municipal public security bureau said in a statement.
The injured person was admitted to hospital for treatment.
Suspect Wang Taicun, a native of east China's Shandong province, was arrested in the area an hour later.
He confessed to police that he had come to Beijing to gain the attention of local authorities concerning personal matters, Xinhua reported.
This is the second incident involving a foreigner in the last few days.
A Britisher tourist was recently thrashed by locals when he allegedly attempted to molest a Chinese girl on a road in the night. He was subsequently detained.
