Abstract: The transition Ψ′→KSKL has been observed for the first time using the 14 million Ψ′ events collected by the Beijing Spectrometer of the Beijing Electron-Positron Collider. Based on this, the relative phase between the strong and electromagnetic amplitudes of Ψ′ decays is found to be around±90 degree. Together with improved measurement of the J/Ψ→KSKL branching fraction, Ψ′→KSKLis found to be enhanced compared with the pQCD "12%" rule between Ψ′ and J/Ψ decays. This is a new challenge in the study of charmonium decay dynamics.