The three people who operated the sites were arrested in southern Ho Chi Minh City.
According to reports, one of the sites was first launched in 2008 to offer free downloads of mainstream films.
Sex clips and videos were included the following year when the website's administrators decided they wanted to attract more visitors.
The three accused earned up to 30 million dong ($2,026.90) a month for running the sites — the equivalent of around 18 months' average salary in Vietnam.
The two websites have reportedly been closed.
Communist Vietnam, a one-party state, allows no independent media and controls all print, broadcast and online publications. Authorities have expressed concern about pornographic content online.