Using dithioester as a chain-transfer agent and azobisisobutyronitrile as an initiator, we synthesized amphiphilic poly(styrene-block-acrylamide) [P(St-b-Am)] by the reversible addition-fragmentation chain transfer (RAFT) polymerization method. To improve the heat stability of the block polymers, amphiphilic P(St-b-Am)/organic montmorillonite (O-MMT) nanocomposites were successfully prepared by the addition of O-MMT during the preparation of the block polymer. The nanocomposites were tested by gel permeation chromatography, IR spectroscopy, X-ray diffraction, transmission electron microscopy, and thermogravimetry. As for Polystyrene (PSt)/O-MMT, RAFT polymerization could control the molecular weight and the molecular weight distribution of PSt. PSt/O-MMT was used as a macro RAFT agent to conduct the polymerization of acrylamide, and P(St-b-Am)/O-MMT nanocomposites were prepared. Nanosize layers of montmorillonite were dispersed in the block polymer matrix, and exfoliative nanocomposites were formed. Therefore, the P(St-b-Am)/O-MMT nanocomposites had a better heat stability than before. (C) 2008 Wiley Periodicals, Inc.