The elite Special Task Force commandos took the eighth base in the district of Ampara early Friday after a three-day operation against the Liberation Tigers of Tamil Eelam (LTTE), a local official said by telephone.
Four LTTE members were killed in one clash on Thursday, while in other confrontations the guerrillas withdrew after token resistance, officials said.
There was no immediate reaction from the guerrillas.
In other violence, police said at least two constables were killed in a Claymore bomb attack in northern Sri Lanka on Friday.
The LTTE set off the roadside bomb in the district of Vavuniya as police were on a routine patrol, a police spokesman said.
He said another policeman was killed on Thursday evening in a confrontation with Tiger rebels in the same area.
More than 60,000 people have been killed in Sri Lanka's Tamil separatist conflict in the past 35 years and diplomatic attempts to end the conflict politically have ended in failure.
Government troops and