Ambassador Joslyn Whiteman said he reported the incident to the Chinese Foreign Ministry and was told they were looking into it.
Whiteman's son, 22-year-old Joslyn Paul Whiteman, was among a group of men rounded up early Saturday in the capital's Sanlitun area, a warren of bars popular among Chinese and expatriates.
An American who witnessed the raid said two to three dozen people were detained, all black, with police using varying degrees of force to restrain them, including beating some with rubber truncheons.
The American, who asked not to be identified because he feared police retaliation, said police first seemed to go after specific people involved in the area's drug trade but then began rounding up all blacks. He said police forced him to delete a picture of the raid he took with his digital camera.
His account was corroborated by online postings and other accounts of the episode.
An officer who answered the telephone at the Sanlitun Police Station said he was unclear about the case. The information office of the Beijing Public Security Bureau, the capital's police, did not respond to a faxed request Wednesday for information about the raid.
Beijing is in the midst of a massive cleanup campaign ahead of next August's Olympics. Drug dealers, many of them African, have been a noticeable presence in the Sanlitun area in recent years, offering marijuana and Ecstasy and other club drugs.
On Monday, Hong Kong's South China Morning Post newspaper quoted Thabo Lieket, a 24-year-old student from Lesotho, as saying he was just walking down the street with friends when he was detained. He was released without charge, it said.
Whiteman's father said his son suffered a concussion from being hit over the head with a rubber baton and was hospitalized for about 10 hours after being released from jail Saturday morning with no charges filed against him.
"He was taken into custody and, according to him, he was not questioned," the ambassador said. "He was dumped in a cell with others and released later."
The ambassador said when he went to the jail to pick up his son, he saw "quite a few people of color" but he said it was not clear whether the raid solely targeted blacks.
African students, who have come to China for decades to study in universities, frequently complain about racism and stereotyping. Racial tensions with ordinary Chinese have occasionally boiled over into fights and protests.