The　dynamic　properties,　including　the　dynamic　mechanical　properties,　flex　fatigue　properties,　dynamic　compression　properties,　and　rolling　loss　properties,　of　star-shaped　solution-polymerized　styrene-butadiene　rubber　(SSBR)　and　organically　modified　nanosilica　powder/star-shaped　styrene-butadiene　rubber　cocoagulated　rubber　(N-SSBR),　both　filled　with　silica/carbon　black　(CB),　were　studied.　N-SSBR　was　characterized　by　H-1-NMR,　gel　permeation　chromatography,　energy　dispersive　spectrometry,　and　transmission　electron　microscopy.　The　results　show　that　the　silica　particles　were　homogeneously　dispersed　in　the　N-SSBR　matrix.　In　addition,　the　N-SSBR/SiO2/CB-rubber　compounds＇　high　bound　rubber　contents　implied　good　filler-polymer　interactions.　Compared　with　SSBR　filled　with　silica/CB,　the　N-SSBR　filled　with　these　fillers　exhibited　better　flex　fatigue　resistance　and　a　lower　Payne　effect,　internal　friction　loss,　compression　permanent　set,　compression　heat　buildup,　and　power　loss.　The　nanocomposites　with　excellent　flex　fatigue　resistance　showed　several　characteristics　of　branched,　thick,　rough,　homogeneously　distributed　cross-sectional　cracks,　tortuous　flex　crack　paths,　few　stress　concentration　points,　and　obscure　interfaces　with　the　matrix.　Accordingly,　N-SSBR　would　be　an　ideal　matrix　for　applications　in　the　tread　of　green　tires.　(c)　2014　Wiley　Periodicals,　Inc.　J.　Appl.　Polym.　Sci.　2014,　131,　40348.