“She will only make it worse,” Trump wrote on his social networks.
His words are quoted by RIA Novosti.
According to the ex-president, Pelosi's involvement in the Taiwan issue is aimed at "creating problems" as well as trying to "make money."
The Financial Times previously wrote that Pelosi plans to visit Taiwan in August to "show support for Taipei."
If the visit goes ahead, it will be the first visit by a speaker of the US House of Representatives to Taiwan in 25 years.
The Chinese Foreign Ministry, in turn, demanded that the US cancel Nancy Pelosi's visit to Taiwan.
The Chinese Defense Ministry said that the Chinese army will not watch this "with folded hands", but "will definitely take all measures to prevent external interference."