The widely used K-profile model developed by Troen and Mahrt (1986) was examined by utilizing the large eddy simulation (LES) data for the shear and buoyancy driven boundary layer. Based on the analysis several important modifications of the model were suggested. First, the profiles of the velocity scale and the Prandtl number in the boundary layer were suggested, contrary to the constant values used in the Troen and Mahrt model. Second, the heat flux due to the entrainment at the inversion layer was incorporated into the K-profile, and it was used to predict the growth of the boundary layer directly. For this purpose new parameterizations for the entrainment and the boundary layer height were suggested. Finally a nonlocal mixing of momentum was included, and its magnitude was parameterized. The effects of the modification were also examined by comparing the results from the two PBL models with the LES data. The new model not only results in the better agreement with the LES data, but also provides the consistency with the existing theory of the PBL.