Clube Atletico Operário, commonly former EC Operário de Mafra, is a Brazilian football club based in Mafra, Santa Catarina state.

The club was founded on May 12, 1897,[1] is Clube Atlético Operário, in the 1990s it was renamed to Sociedade Esportiva e Recreativa Operários Mafrenses, but the club's logo still depicts the acronym CAO, meaning Clube Atlético Operário.

[2] They won the Campeonato Catarinense Third Level in 1913, 1947, 1996.

[2] Clube Atlético Operário play their home games at Estádio Alfredo Herbst.

[1] The stadium has a maximum capacity of 3,000 people.