He was going to see friends in Shenzhen and was expected to return to Hong Kong the next day. But he never did.
A second US-based academic has been arrested while on a trip to China.
Li Shaomin was detained a month ago during a brief visit to the southern city of Shenzhen.
The Chinese government has so far refused to make any comment on why he was detained or where he is being held.
Dr Li is originally from China but has been a US citizen for six years.
Beijing and Washington are already engaged in a diplomatic dispute over another academic, Gao Zhan, who was detained last month.
Regular traveller
According to Li Shaomin's wife, her husband crossed the border from Hong Kong on 25 February.
He was going to see friends in Shenzhen and was expected to return to Hong Kong the next day. But he never did.
The US embassy in Beijing has confirmed that a US citizen is being held, but the Chinese government is so far refusing to say anything about why Dr Li has been detained.
He teaches business and management at the City University of Hong Kong.
His wife told the BBC he travels to China regularly, both to teach and as a consultant.
Bitter row
She said she could not think of any reason why the Chinese authorities would want to arrest him.
News of Dr Li's arrest comes as China and the United States are already embroiled in a bitter row over the fate of Gao Zhan, another US-based academic who was detained on a visit to Beijing last month.
China has accused Gao Zhan of spying.
Gao is only a US resident and so does not enjoy the full protection of the US government.
President Bush has called on Beijing to release her and members of the US Congress are trying to have Gao granted full US citizenship even as she languishes in a Beijing detention centre.