Olga Alexandrowna Ladyzhenskaya (Ольга Александровна Ладыженская; born March 7, 1922, Kologriv, died January 12, 2004, St. Petersburg) was a Russian mathematician. She was known for her work on partial differential equations especially Hilbert's 19th problem. She was a student of Ivan Petrovsky.
She provided the first rigorous proofs of the convergence of a finite difference method for the Navier-Stokes equations.
She was awarded the Lomonosov Gold Medal in 2002.