The rheological properties of polybutene-1 with different molecular weight (M (w)) and polydispersity index (PDI) were studied by means of rubber-processing analyzer (RPA). The studies included strain sweeps, frequency sweeps, temperature sweeps, and stress relaxation tests after a sudden shear displacement. It is observed that the linear viscoelastic regions are basically identical for all the samples with different molecular structure and become smaller slightly with increasing frequency. The melts with larger M (w) and/or PDI present higher viscoelasticity moduli, melts viscosity, relaxation modulus, and better temperature stability, but lower loss factor and critical shear rate. Furthermore, it is found that crossover frequency decreases with increasing M (w) and crossover modulus increases with decreasing PDI. In addition, stress relaxation followed by substantial stress growth is observed for the PB-1 melt with larger M (w) in the stress relaxation measurement.