They have been ordered to leave Russia before April 5, Russian news agency TASS reported.
The convoy of vehicles left the diplomatic mission by 7 am Moscow time.
Retired military intelligence officer Skripal, 66, and his daughter, Yulia, 33, were found slumped on a bench in Salisbury city centre on March 4.
On March 26, Washington announced its decision to expel 60 Russian diplomats and close Russia's Consulate General in Seattle as a retaliatory move to the incident of poisoning Russian ex-spy Sergei Skripal and her daughter.
Russia, in response, had made an announcement of expulsion of 58 diplomats from the US Embassy in Moscow and two employees of the US Consulate General in Yekaterinburg, the report said.