The woman was one of two Filipinos arrested for smuggling over 12 kilogrammes of high-grade heroine into China in 2011, Department of Foreign Affairs spokesman Raul Hernandez told reporters.
"President Benigno S. Aquino III has written a letter of appeal to Chinese President Xi Jinping requesting a commutation of the death sentence," Hernandez said.
He said the letter was delivered to Chinese diplomats today, but the execution was still expected to be carried out between tomorrow and Tuesday next week.
The Filipino male companion caught with her had also been handed a death penalty. However it came with a two-year reprieve, which means the sentence can be commuted.
Also Read
The scheduled execution could further complicate already rocky bilateral relations between the two countries soured by overlapping territorial claims in the South China Sea.
In March 2011, China executed three Filipino drug mules despite repeated pleas by the Philippine government and the Catholic church.
The executions triggered widespread condemnation in the Philippines, which abolished death sentences in 2006.
He also emphasised the Philippines "respected" Chinese law and the top court's decision in the case.
"The Philippine government itself has a strong anti-illegal drug policy, and is closely cooperating with law enforcement agencies in China and in other countries on efforts against drug trafficking," he said.
About a tenth of the country's 100 million population work abroad, many of them under harsh conditions where drug traffickers sometimes exploit them into becoming drug mules.
Hernandez said that there were 213 Filipino ensnared in drug-related cases in China.