Nanofibrils of ultrahigh molecular weight syndiotactic polystyrene (sPS) have been synthesized in a silica nanotube reactor (SNTR) using a metallocene catalyst in conjunction with methylaluminoxane cocatalyst. Very thin sPS nanofibrils (< 10 nm) grown at the catalytic sites on the pore walls aggregate to form intertwined, rope-like nanofibrils with 30-50 nm diameters, which further intertwine into even larger 200 nm diameter polymer nanofibrils. The extrusion of nanofibrils synthesized inside the SNTR was directly observed by scanning electron microscopy, and the individual SNTR containing a single polymer nanofibril was separated and observed by transmission electron microscopy. The sPS synthesized in the SNTR has ultrahigh molecular weight (M-w = 928 000 g/mol) with a large fraction of 2 000 000-5 000 000 g/mol molecular weight polymers.