Effect of layered silicates on structure of microfibrillar composites (MFCs) with reinforcing PA6 fibrils formed in situ by melt drawing was studied. Clay was added to HDPE/PA6 MFC using different mixing protocols including simultaneous addition, application of pre-made masterbatches with both constituents and their combinations. In all cases, majority of nanofiller (NF) was contained inside PA6 fibrils. On the other hand, fibrils dimensions were significantly affected by the clay addition protocol; their marked increase in the case of simultaneous addition of all components and application of HDPE/C30 nanocomposite indicate important effect of NF migration to the PA6 phase in the course of mixing and melt drawing. The effect of properties of PA6 and HDPE phases and NF migration on the morphology evolution is discussed. It is shown that the fiber shape and volume after sample drawing are controlled by the interplay between the dispersed fibril extension and coalescence. POLYM. ENG. SCI., 55:2133-2139, 2015. (c) 2015 Society of Plastics Engineers