US military personnel held four male and four female students after they allegedly entered Osan Air Base near the capital Seoul.
They were later transferred to the custody of South Korean authorities, police said.
The students were being investigated under a law protecting military installations in South Korea, according to police, who said they all had invoked their right to remain silent during questioning.
Police said the students shouted slogans at the site including, "Let's smash US 7th Air Force."
A US military statement said the group attempted to unlawfully enter the base through the main gate and that "unauthorised attempts to access a US military installation are taken extremely seriously."
The incident will be addressed in accordance with applicable US and South Korean laws and procedures, the military said.
The Korean Progressive University Student Union said in a statement those detained were members who were trying to protest what it called the US military's opposition to a South Korean semiconductor cluster project.
South Korean police declined to comment on the group's statement, which was not addressed by the US military.
Yonhap news agency reported the US said it has important interests in a military airport set to be relocated over the semiconductor project.
There are about 28,500 US troops stationed in South Korea to help deter potential aggression from North Korea, a legacy of the 1950-53 Korean War that ended with an armistice, not a peace treaty.
Surveys have steadfastly shown a majority of South Koreans support the US-South Korean military alliance, but the US presence and its role in South Korea's turbulent modern history also have been long-running sources of anti-US sentiment in the country.
South Korean police arrested four students in 2019 who broke into the US ambassador's residence in Seoul while protesting the Trump administration's demands for the country to pay more to help cover the costs of US troops there.
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