Writer Nguyen Quang Lap was detained after police searched his house on Saturday morning and printed several stories from his blog, said Ho Thi Hong, Lap's wife.
"The articles are written by others, and they said some are against the state," Hong said.
Lap's blog could not be accessed as it requires an invitation.
The case follows a sharp increase in arrests and prison terms for government critics in the past few years that has alarmed the United States, a former enemy that is struggling to build a case for deeper trade ties with a country steadfast in its intolerance of dissent.
Lap's detention is the second in the past week. Last Saturday the Police Ministry said blogger Hong Le Tho was detained for posting "bad content" about the state.
(Also see: China jails blogger in online 'rumour' crackdown)
In October, Vietnam released jailed blogger Nguyen Van Hai, who staged a hunger strike to protest treatment of political prisoners.
The popularity of political blogs has grown with increasing Internet usage in the country and simmering discontent over the Communist government's handling of a stale economy and rampant graft.
The Internet has been used as one of only a few channels for dissent in a country where protests are rare and the media is tightly controlled by the state.
The United States has urged improvements in Vietnam's human rights record. In an address to Congress in June, the U.S. State Department's envoy for democracy, Daniel Baer, described Vietnam's crackdown on bloggers as part of "a years'-long trend of deterioration".
© Thomson Reuters 2014
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