"The Chinese side has all along opposed any official exchanges and military cooperation between the Untied States and Taiwan," a foreign ministry spokesman said.
"We express our serious concern and have raised solemn representations with the American side."
Allen, who is in charge of Asia Pacific affairs in Rumsfeld's office, could become the most senior active US military officer to visit Taiwan in 25 years, if his trip proceeded as reported.
"We strongly urge the US side to abide by the position repeatedly stated by the leaders of the United States," the spokesman said.
"And take real actions to carry out their commitments on the one China policy..., and end official exchanges and military cooperation with Taiwan and stop military sales to Taiwan."
According to the China Times Express, Allen was to meet with Taiwan military authorities in a trip that would mark a departure from US policy, which bans Taiwan visits by any US generals on duty.
Taiwan's defense ministry declined to comment on the report.
Washington shifted its diplomatic recognition from Taipei to Beijing in 1979 but remains the leading arms supplier to the island, despite China's objection.
China claims sovereignty over Taiwan, which split from the mainland after a civil war in 1949, threatening to use force if the island sought formal independence.
The re-election in March of Taiwan's independence-leaning President Chen Shui-bian has enraged Beijing which has racheted up its war-like rhetoric.
In a report released in late May, the US Defence Department warned China was developing "credible military options" to prevent Taiwanese independence, including tools to discourage the United States from coming to the island's aid in a conflict with the mainland.
Pentagon analysts say Chinese missiles could feasibly destroy key Taiwanese leadership facilities, military bases and infrastructure with minimal advance warning.
Some are believed to be capable of hitting US military bases in Japan.