The officer has been identified only as Hoang, a 35-year-old manager of a warehouse used to store contraband by the Hanoi Customs Department, which said it is treating the case as “extremely serious.”
Hoang's crime was discovered in April, but the department only published an official statement this week.
Its chief officer told local media on August 15 that Hoang had colluded with two other people to replace the ivory with a fake batch. The tusks were being stored to be used as exhibits in the smuggling case.
The two accomplices have also been arrested. Their identities have not been revealed, but the authorities said they don't work for the customs agency.
The global trade in elephant ivory has been widely outlawed since 1989 after populations of the African giants dropped from millions in the mid-20th century to around 600,000 by the end of the 1980s, AFP reported.
The population is now believed to be some 415,000, with 30,000 illegally killed each year.
Elephant ivory can fetch up to US$1,100 per kilogram (2.2 pounds), the report said.
Vietnam outlawed the ivory trade in 1992, but the country remains a top market for ivory products used for decorative purposes or in traditional medicine, despite the lack of scientific evidence.
The country is also a busy transit point for tusks trafficked from Africa to China and other parts of Asia.