Amnesty International has condemned the executions of two Japanese men in the first death sentences carried out since the country's new government came to power last year.
Alan Shadrake was arrested for criminal defamation after he published a book critical of the country's use of the death penalty.
President Ma Ying-jeou urged to ensure that the country's de facto moratorium on executions remains in place.
Speaking at an anti-death penalty summit in Geneva, Amnesty International's interim Secretary General Claudio Cordone hailed global efforts but said more needs to be done.
In a five to four ruling, the Court stated that capital punishment did not violate "human dignity and worth" protected in the Constitution.