The series of HTPB (hydroxyl terminated polybutadiene)/organoclay nanocomposite was formed by melt blending with rotationary and revolutionary mixer which generated high shear stress. Organoclays were formed by modifying the pristine clays with organic modifiers which had different hydrophobic chain lengths. As the length of organic modifier increased, the gap size between layers of organoclay became broader. The clays modified with octadecylamine (C18) and dodecyl amine (C12) showed wider gap sizes than that modified with octyl amine (C8). This gap size affected the dispersion state of clays, exfoliation/intercalation in HTPB polymer medium. The mixtures of HTPB with C18 and C12 were transparent without sedimentation and showed almost exfoliated structure. HTPB/C18 mixture showed the higher viscosity and yield strength than HTPB/C12 due to exfoliation. HTPB/C12 showed more elastic behavior than HTPB/C18 mixture because the organoclay C12 had less content of organic modifier. (C) 2008 Elsevier Ltd. All rights reserved.