J Glob Optim (2008) 40:277–288 DOI 10.1007/s10898-007-9197-2 On the interior regularity of weak solutions to the non-stationary Stokes system Joachim Naumann · Jörg Wolf Received: 30 May 2007 / Accepted: 9 June 2007 / Published online: 26 July 2007 © Springer Science+Business Media, LLC 2007 Abstract In this paper, we prove that any weak solution to the non-stationary Stokes system in 3D with right hand side -div f satisfying (1.4) below, belongs to C ( ]0, T [; C α ()). The proof is based on Campanato-type inequalities and the existence of a local pressure introduced in Wolf [13]. Keywords Non-stationary Stokes system · Interior regularity Mathematics Subject Classification (2000) 35Q30 · MSC 35D10 1 Introduction. Statement of main result Let be a bounded domain in R 3 , let 0 < T < and define Q := ×]0, T [. We consider the Stokes system u t - u +∇ p =-div f in Q, (1) div u = 0 in Q, (2) where u = (u 1 , u 2 , u 3 ) denotes the velocity vector, p the pressure and -div f an external force. Proc. Conference “Variational analysis and PDE’s”. Intern. Centre “E. Majorana”, Erice, July 5–14, 2006. J. Naumann · J. Wolf (B ) Humboldt-Universität zu Berlin, Institut für Mathematik, Unter den Linden 6, 10099 Berlin, Germany e-mail: jwolf@mathematik.hu-berlin.de J. Naumann e-mail: jnaumann@mathematik.hu-berlin.de 123