The transition points of the boundary layer on NACA 0012 airfoil surface were measured by the flow visualization technique with China clay as well as the surface Pitot method. The former and the latter predict the transition point and the transition region, respectively. Both data do not contradict each other in the sense that the transition point of the former lies within the transition region of the latter, but definite trend has not been found as to what part of the latter transition region the former transition point corresponds.
The measured transition data have been compared with the theoretical transition points predicted by Michel's and Granville's criterions for transition point, respectively. Michel's criterion often predicts the starting point of the transition and Granville's on the contrary, predicts the fianl point of the region. The agreements are generally satisfactry.

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