Mauritian Prime Minister Navin Ramgoolam has become the third leader to announce a boycott of this week's Commonwealth summit in Colombo over Sri Lanka's human rights record.
Indian Prime Minister Manmohan Singh and his Canadian counterpart Stephen Harper are also staying away.
Sri Lanka is accused of committing widespread abuses in the final months of its war against Tamil Tiger rebels.
The Sri Lankan government strongly denies the claims.
Mr Ramgoolam told Mauritius' parliament on Tuesday that he would not attend the meeting and that Mauritius will instead be represented by Foreign Minister Arvin Boolell.
"My information that I have tried to get from different quarters is that the Sri Lankan Government is not doing enough," Mr Ramgoolam told parliament, referring to Sri Lanka's human rights record.
"I cannot, with the principle that I have taken all this time I am in politics, attend the summit," he added.
Mr Boolell told the BBC's Tamil Service he did not think the decision would adversely affect relations between the two countries.
Menon Murday, a representative of the Tamil community in Mauritius, was quoted as welcoming Mr Ramgoolam's decision.
India also announced earlier this week that Mr Singh would not go to the summit, and that India's foreign minister would attend instead.
Correspondents in Delhi say there had been growing pressure on Mr Singh to boycott the summit, especially from Tamil politicians in India.
In October, Mr Harper said he had not taken the decision to boycott the meeting lightly.
But he said a lack of accountability for human rights abuses "during and after the civil war is unacceptable".
Canada is home to the largest expatriate Sri Lankan Tamil community. Many migrated over the past few decades as civil war gripped Sri Lanka.
Sri Lanka's army defeated the ethnic-Tamil rebels after a brutal 26-year war that left at least 100,000 people dead.
Both sides were accused of human rights abuses throughout the conflict, with much focus on its final stages when thousands of civilians were trapped in a thin strip of land in the north of Sri Lanka.
Estimates of civilian deaths in the final months range widely from 9,000 to 75,000.
The Sri Lankan government commissioned its own investigation into the war in 2011.
It cleared the military of claims that it deliberately attacked civilians. It said that there had been some violations by troops, although only at an individual level.