A novel method of developing cocontinuous morphology in 75/25 and 80/20 w/w polypropylene/high density polyethylene (PP/HDPE) blends in the presence of small amount (0.5 phr) of organoclay has been reported. SEM study indicated a reduction in average domain sizes (D) of disperse HDPE when PP, HDPE, and the organoclay were melt-blended simultaneously at 200 degrees C. However, when the two-sequential heating protocol was employed, (that is, the organoclay was first intercalated by HDPE chains at 150 degrees C, followed by melt blending of PP at 200 degrees C), very interestingly a cocontinuous morphology was found even for very asymmetric blend compositions. WAXD study revealed the intercalation of both PP and HDPE chains inside the clay galleries, when PP/HDPE and clay were melt-mixed together at 200 degrees C. However, when the two-sequential heating protocol was used the organoclay platelets were selectively intercalated by the HDPE chains. Addition of SEPS in the blend decreased the D of HDPE domains in both the blending methods. Thus, the observed cocontinuous morphology in asymmetric composition of PP/HDPE blend in presence of clay is because of the barrier effect of the clay platelets in the HDPE phase that restrict the phase inversion into the domain/matrix morphology. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 3080-3092, 2011