Portrait of Irma Sèthe is an oil on canvas painting by the Belgian neo-impressionist painter Théo van Rysselberghe.

The work is a portrait, painted in pointillist style, of Irma Sèthe, one of the heiress of a musical Brussels family close to the painter, playing the violin.

While Van Rysselberghe was not the first member of Les XX to produce work based on the guidelines set by Seurat, he nevertheless ended up with being to most committed to the latter, sticking with divisionism for the rest of his career.

In Portrait of Irma Sèthe (who was Alice's sister) Van Rysselberghe cemented his newly discovered style.

Maria played the harmonium and Irma was apprenticed to the "King of Violin" Eugène Ysaÿe, a violinist and teacher at the Royal Conservatory of Brussels.

Van Rysselberghe made a great impression on his fellow painters with his Portrait of Irma Sèthe, especially on Paul Signac, who described it in his diary as "extraordinarily delicate."