Tuesday's extension was passed in parliament without voting as most of the parliamentarians were absent to campaign for the March 30 local elections.
Rantasiri Wickremanayake, the prime minister, told parliament: "Last month, the killings and attempted killings came down.
"This is a good trend. We want it to continue and so we need to extend the state of emergency."
Wickremanayake said there had been only 10 killings and nine attempted killings since the two sides met last month in Switzerland for their first high-level talks since 2003, a vast improvement than earlier in the year.
The army said that no soldiers were wounded last month.
But divisions between the two sides remain vast. Mahinda Rajapakse, has repeatedly ruled out Tiger demands for a Tamil homeland and the rebels have threatened a return to a two-decade war that has killed more than 64,000 if they do not win concessions.
About 200 people died in December and January as suspected Liberation Tiger of Tamil Eelam (LTTE) attacks on the military almost destroyed a ceasefire declared in 2002, but officials say violence has since eased.
Sri Lanka first imposed a state of emergency after the assassination of its foreign minister by a suspected Tiger assassin six months ago.
The state of emergency, which was extended first for a presidential election in November and then every month since, gives the police and army wide powers.