In this study, polyindene (PIn) and three PIn/organo-montmorillonite (O-MMT) nanocomposites namely K1: [PIn(94.5%)/O-MMT(5.5%)], K2: [PIn(92.8%)/ O-MMT(7.2%)], and K3: [PIn(87.9%)/O-MMT(12.1%)] were used to investigate the electrorheological (ER), creep-recovery, and vibration damping characteristics. A volume fraction series (u ¼ 5-25%) of suspensions were prepared from the samples in silicone oil (SO). First, zeta (f)-potentials and antisedimentation stabilities; second, ER properties of these nanocomposite/SO suspension systems were determined under externally applied electric field strengths. Besides, the effects of dispersed phase volume fraction, shear rate, electric field strength, and temperature onto ER performance of these suspensions were investigated and non-Newtonian rheological behaviors were observed. The vibration damping capabilities of the suspensions were investigated using various rheological parameters on the electrorheometer and on an automobile shock absorber and a 66% vibration damping capacity were determined under an applied electric field strength, which is an important property from industrial point of view. Furthermore, the materials were subjected to creep and creeprecovery tests and reversible viscoelastic deformations were determined. From the experiments carried out, the nanocomposites were classified as smart materials.