In this paper, an adjoint-based error estimation and grid adaptation study is conducted for two-dimensional viscous flow with unstructured hybrid meshes. The error in an integral output functional of interest is estimated by a dot product of the residual vector and adjoint variable vector. Regions to be adapted are selected based on the local error of each node. The adaptive regions are refined by the regular refinement algorithm. The present procedure is applied to a two-dimensional low-speed viscous flow around the 30P30N multi-element airfoil at high incidence angle (α=21deg.). The same level of prediction accuracy for lift and drag is achieved with much less mesh points than uniformly refined fine meshes. The accuracy of error estimation is improved with residual smoothing strategy as effectively as with that for inviscid flow cases.