This paper is concerned with non-stationary flows of shearthinning fluids in a bounded two-dimensional C 2,1 domain. Assuming perfect slip boundary conditions, we provide a proof of the existence of a solution with the Hölder continuous velocity gradients and pressure under condition that a stress tensor satisfies power-law with growth p ∈ [5/3; 2].Mathematics Subject Classification (2010). 35B65, 35K51, 35Q35, 76D03.