Sony Lab'ou Tansi (5 July 1947 – 14 June 1995), born Marcel Ntsoni, was a Congolese novelist, short-story writer, playwright, and poet in French language.

He was initially educated in the local language, Kikongo, and only began speaking French at the age of twelve, when his family moved to Congo-Brazzaville, today known as the Republic of the Congo.

When the young teacher began writing for the theatre later that year, he adopted the pen name "Sony La'bou Tansi" as a tribute to Tchicaya U Tam'si, a fellow Congolese writer who wrote politically charged poetry about oppressive nature of the state.

In 1979 he founded the Rocado Zulu Theatre, which would go on to perform his plays in Africa, Europe, and the United States in addition to appearing regularly at the Festival International des Francophonies in Limoges.

In that same year, Tansi was elected to parliament as a deputy for the Makélékélé arrondissement of Brazzaville, but his participation in opposition politics angered President Lissouba, and his passport was withdrawn in 1994.