Aquino said he had tried in vain to contact China's leader over the case, and said he would send Vice President Jejomar Binay to Beijing to convey his personal request to spare the two women and a man.
The trio -- who would be the first Philippine nationals executed in China -- were convicted separately of smuggling heroin into China in 2008, the foreign department said.
"I am trying to set up a phone conversation with President Hu Jintao again to make an appeal for the commutation" of the death sentences, Aquino told reporters.
He said Filipino diplomats had been trying to patch him through to Hu since Friday. "As of now, they (Beijing) have not signified willingness to accept the phone call.
"But we think our request is very, very reasonable. It is time for them to demonstrate their pronounced statements of improved closer bilateral ties. This will be a test (of that)," Aquino said.
The condemned 42-year-old Filipino man and 32-year-old woman were both convicted in December 2008 while the third, a 38-year-old woman, was sentenced in May 2008.
The first two are scheduled to be executed on Monday in the southern city of Xiamen and the 38-year-old woman in Shenzhen, near Hong Kong, on Tuesday, officials said.
However, the Chinese embassy in Manila showed no sign of its government relenting.
"The death sentence on the three Filipino drug traffickers is the final verdict by the Chinese judicial authorities in accordance with law," it said in a statement Wednesday.
"As criminals (facing the) death penalty, their legitimate rights and interests have been protected in accordance with law."
The embassy would help relatives who may want to visit the three in prison before their execution, the statement said, adding that it hoped the case would not affect diplomatic ties.
Aquino said many Chinese drug traffickers had been arrested in the Philippines but could not face execution because the mainly Roman Catholic nation had abolished capital punishment.
"We'd like to see reciprocity, hopefully," he said.
The scheduled executions come after ties chilled over the deaths of eight Hong Kong Chinese in a bungled bus hostage rescue in Manila late last year.
Officials in Hong Kong were disappointed by Aquino's subsequent decision to slap minor criminal charges against several police officials involved in the fiasco.