To produce a 1,2-polybutadiene as a thermoplastic elastomer which allows no generation of mold stains, thermal degradation nor change in physical properties with time at high-temperature molding and exerts excellent properties such as moldability, transparency, mechanical strength property, wet skid resistance, and a 1,2-polybutadiene which yields a vulcanized rubber having excellent properties.

A 1,2-butadiene has (i) a 1,2-bond content in a bond unit of butadiene of 70 wt.% or larger, (ii) a melting point within the range of from 50 to 130°C, (iii) a viscosity η, measured by using a slit die rheometer at a shear rate of 5,113 sec-1, of from 400 to 1,200 poise at 120°C, from 300 to 1,000 at 150°C and from 200 to 800 poise at 180°C and (iv) a total halogen content of 30 ppm or smaller.