In current study, a real-time rheological method was used to investigate the intercalation and exfoliation process of clay in high-density polyethylene/organoclay (HDPE/OMMT) nanocomposites using maleic anhydride grafted polyethylene (PEgMA) as compatibilizer. To do this, a steady shear was applied to the original nonintercalated or slightly intercalated composites prepared via simple mixing. The moduli of the composites were recorded as a function of time. The effect of matrix molecular weight and the content of compatibilizer on the modulus were studied. The role of the compatibilizer is to enhance the interaction between OMMT and polymer matrix, which facilitates the dispersion, intercalation, and exfoliation of OMMT. The matrix molecular weight determines the melt viscosity and affects the shear stress applied to OMMT platelets. Based on the experimental results, different exfoliation processes of OMMT in composites with different matrix molecular weight were demonstrated. The slippage of OMMT layers is suggested in low-molecular weight matrix, whereas a gradual intercalation process under shear is suggested in high-molecular weight matrix. Current study demonstrates that real-time rheological measurement is an effective way to investigate the dispersion, intercalation, and exfoliation of OMMT as well as the structural change of the matrix. Moreover, it also provides a deep understanding for the role of polymer matrix and compatibilizer in the clay intercalation process. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 302-312, 2010