Male EFF MPs, dressed in red overalls and hard hats, sang and danced in front of the steps of the National Assembly where they were due to be sworn in.
Most female EFF MPs chose to dress as cleaners in red dust coats with aprons, and brightly coloured headscarves.
New EFF MP Magdalene Moonsamy said she was excited to be in Parliament.
Moonsamy, unlike her EFF colleagues, wore a red skirt and red knitted top.
Representing working class
Explaining the symbolism, EFF MP-in-waiting Floyd Shivambu said: "The working class and poor now know they've got representatives in Parliament. There is no other organisation which associates itself with the struggles of the poor."
Shivambu said the EFF dress code was deliberate.
Unlike during election campaigning when EFF members wore overalls displaying the party's name, Wednesday's uniforms were bare of party insignia.
Parliament has said MPs should observe the decorum of the House by not displaying party political insignia during sittings.
MPs from other parties walking into the National Assembly building chose the traditional suit and tie, or dress suits for women, for the swearing in ceremony, due to start at 10:30.
Speaking to News24 outside Parliament, the EFF's Floyd Shivambu said the EFF has not "sold out" and that the nationalisation of mines and land expropriation without compensation remains a priority. Watch: