Rosina Cox Boardman (1878–1970) was an American painter of portrait miniatures and botanical illustrations.
Born in New York City, Boardman was a descendent of several of the oldest families in the state, including the Livingstons and Schuylers. She studied at the Art Students League of New York, the New York School of Applied Design, and the Chase School of Art; among her instructors were George Bridgman, Frank Vincent DuMond, and Alice Beckington. She often showed her work and won prizes, including, in 1930 and 1938, the Levantia White Boardman Memorial Medal of the American Society of Miniature Painters, which she had endowed in honor of her mother. In 1933, she was called by Time Magazine one of the best miniaturists in the country; due to her application of contemporary techniques, such as those learned from Virginia Richmond Reynolds, she was also described as a rebel. Several works by Boardman, including a self-portrait, are in the collection of the Metropolitan Museum of Art, and others are in the Worcester Art Museum. A portrait of her teacher Alice Beckington is currently owned by the Smithsonian American Art Museum, which also owns portraits of her by Lydia Longacre and Mabel Rose Welch.