The RMT union has been fighting the further extension of driver-only operation by Govia Thameslink Railway since April 2016, holding numerous walkouts over access and safety concerns.
GTR says that Southern services on most routes will operate normally.
A reduced Brighton to Hove shuttle service will run, while a small number of cancellations are expected in the Bognor Regis, Littlehampton, Brighton, West Worthing and Portsmouth areas.
Mick Cash, general secretary of the RMT, said; “Our members stand solid and united again today in the fight for passenger safety and access on Southern Rail in Britain’s longest-running industrial dispute.”
Last month when the strike date was announced, a spokesman for Southern said: “The RMT strike will have no impact on the vast majority of passengers as we expect to run a normal service on most routes.
“Only last week the RMT rejected proposals we made about the basis for finding a settlement and we renew our call for the union to end this pointless dispute.
“The RMT should face the reality that the changes they are objecting to were successfully introduced a year ago.”
For more information visit Southern’s website