An axisymmetric air free shear layer was experimentally investigated in order to determine the effect of the initial peak fluctuation levelu′pe/Ueon the characteristic measures of the free shear layer. The shear layer width and the similarity parameter depend noticeably onu′pe/Ue. The asymptotic peak turbulence intensityu′p∞increases withu′pe/Uebut appears to have a limiting value of about 0.18. The location for achievement of self‐preservation progressively moves upstream with increasingu′pe/Ue, suggesting that higher initial fluctuations hasten the spectral evolution of the velocity fluctuations and development of the shear layer. The results show that the initial fluctuation level has a much more dramatic effect on the evolution and the average characteristic measures of the free shear layer than the initial momentum thickness has, and may have been the primary reason for discrepancies among results from different previous inverstigations.