Polybutadiene rubber (BR)/clay/dimethyl dihydrogenatetallow ammonium chloride (DDAC) composites were prepared by a new preparation method named in situ organic modification. That is, BR, pristine clay, and quaternary ammonium salt were directly melt-mixed without the usual pretreatment of the pristine clay with an intercalatant. BR/pristine clay, BR/organoclay DK4 (modified with DDAC), and BR/clay/DDAC composites were analyzed with X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis. The vulcanization characteristics and mechanical properties of the BR/pristine clay, BR/DK4, and BR/clay/DDAC composites were investigated. Finally, the effects of the processing conditions, clay/DDAC ratio, and clay content on the structure and properties of the BR/clay/DDAC composites were investigated. The results showed that intercalated BR/clay/DDAC composites were prepared. Organoclay DK4 and clay/DDAC effectively accelerated the vulcanization reaction of BR, which was attributed to the existence of the intercalatant used to modify the clay. The tensile strength, elongation at break, and tear strength of the BR/clay/DDAC vulcanizates were greatly improved in comparison with those of gum BR and BR/pristine clay vulcanizates but were somewhat lower than those of BR/DK4 vulcanizates. The dispersion of clay particles in the BR/clay/DDAC and BR/DK4 composites was much better than that in the BR/pristine clay composite. The temperature at the thermal degradation peak of the BR/clay/DDAC composite obviously increased in comparison with those of the gum BR, BR/clay and BR/DK4 composites. The mixing temperature and rotor speed had remarkable effects on the structure and properties of the BR/clay/DDAC composite. (c) 2005 Wiley Periodicals, Inc.