And it amounted to the latest extraordinary effort by Trump to openly request political assistance from foreign governments.
Thursday's comments weren't the first time Trump has injected Biden into his relationship with China, though he said Thursday he has never pushed Xi to investigate the former vice president.
In that call, Trump also told Xi he would remain quiet on Hong Kong protests as trade talks progressed.
Asked earlier this week about Trump's call with Xi, the White House did not deny that he raised Biden.
"It's certainly something we can start thinking about," Trump said when questioned whether he would seek the help of Xi in investigating Biden.
Biden was tasked during the Obama administration with courting then-Vice President Xi during his apprenticeship for China's top job.
"I've spent as much time with Xi Jinping as anybody has," Biden has boasted on campaign trail, hoping to burnish his foreign policy credentials. »