An approach for evaluating residual stresses in thin films by critical buckling observation of circular microstructures is proposed, by which the states of residual stresses can be distinguished directly from the observed critical buckling patterns and their magnitudes can be estimated with finite element method after the critical etching length is measured. For practical operation, three samples were prepared by surface micromachining technique and a specially designed video system was set up for in-situ monitoring the whole process during the sacrificial layer etching. Then, measurements of residual stresses were performed and the results were compared with those obtained from micro rotating structures. As a result, the approach is proved to be relatively simple, both compressive and tensile residual stresses with wide range of amplitude can be evaluated by just using a single appropriately designed circular microstructure. (C) 2008 Elsevier B.V. All rights reserved.