In this communication, we report the first rheological study on the chain‐straightened Ni‐diimine poly(1-hexene)s and investigate the unique effect of chain straightening on plateau modulus and entanglement molecular weight of this series of polymers. Two Ni-diimine poly(1-hexene) samples having different levels of chain straightening were prepared with a chain‐walking Ni‐diimine catalyst, (ArN?C(An)?C(An)?NAr)NiBr₂ (An?=?acenaphthene, Ar?=?2,6-(i‐Pr)₂C₆H₃₎ at two different temperatures. Rheological analyses show that the chain‐straightened polymers exhibit significantly enhanced plateau modulus and reduced entanglement molecular weight compared to regular poly(1‐hexene)s by metallocene catalysis. Such an effect becomes more pronounced with an increase in the level of chain straightening.