Saridewi Djamani, 45, was sentenced to death in 2018 for trafficking nearly 31 grams (1.09 ounces) of heroin, the Central Narcotics Bureau said.
It said the amount was “sufficient to feed the addiction of about 370 abusers for a week”.
Human rights groups, international activists and the United Nations have urged Singapore to halt executions for drug offenses, saying there is increasing evidence it is ineffective as a deterrent.
But its authorities insist capital punishment is important to halt drug demand and supply.
Singapore’s laws mandate the death penalty for anyone convicted of trafficking more than 500 grams (17.64 ounces) of cannabis and 15 grams (0.53 ounces) of heroin.
It has executed 15 people for drug offenses since it resumed hangings in March 2022, an average of one a month, human rights groups say.
Djamani’s execution comes two days after a Singaporean man, Mohammed Aziz Hussain, 56, was executed for trafficking around 50 grams (1.75 ounces) of heroin.
The narcotics bureau said both prisoners were accorded due process, including appeals against their convictions and sentences, and petitions for presidential clemency.
Anti-death penalty campaigners said the last woman known to have been hanged in Singapore was Yen May Woen, a 36-year-old hairdresser, also for drug trafficking, in 2004.