Polyolefin blend type thermoplastic elastomers (TPEs) were prepared via melt blending method in a twin screw extruder by using isotactic polypropylene (i-PP), three different styrene-olefin triblock copolymers (SEBS-1 and SEBS-2 having a styrene content of 30 wt.% and 60 wt.%, respectively and SEEPS having a styrene content of 30 wt.%) and paraffinic oil. Composition-dependent and time-dependent viscoelastic properties of compounds were determined by various test procedures conducted in a rotational rheometer in melt state. It was found that the content of polystyrene blocks (or hard segment) in copolymers governed the rheological behaviors of compounds. It can be concluded that the increasing amount of styrene-olefin block copolymer or content of glassy domains into blend composition reduces miscibility between polyolefin and elastomer phases and also yields higher melt elasticity and viscosity, longer relaxation times, lower creep strain and compliance values at relatively longer time scale.