Sina (Sientje) van Houten (Groningen, 23 December 1834 – The Hague, 20 March 1909) was the wife of Hendrik Willem Mesdag, the Dutch marine painter of the Hague School, and a painter herself.
She was the eldest of seven children of Derk van Houten en Barbara Elisabeth Meihuizen. One of her brothers was later Minister Samuel van Houten. Her father had a large sawmill on the Damsterdiep. She married Mesdag on April 23, 1856.
Sientje was a strong moral support to her husband, especially when she enthusiastically supported him in 1866, when he gave up his business profession solely for painting. She began to paint in 1879, after she lost her only child, the 8-year-old Klaas. Gerkens Arnaud helped her drawing, while the painting was aided by her husband and her cousin Lawrence Alma-Tadema.
In 1881 she took part in painting the Panorama Mesdag. In 1884, one of her landscapes won a gold medal in Amsterdam she received a bronze medal in Paris for a heath landscape. In 1893 she made a big impression at an exhibition in Chicago. When Sientje Mesdag was 70 years, in 1905, she had an honorary exhibition in the halls of the Pulchri Studio.