Abstract Polymorphic crystallization behaviors in amorphous/crystalline polymer blends of cis-1,4-polyisoprene/trans-1,4-polyisoprene (CPI/TPI) have been not fully understood so far. In this work, we investigated the effects of CPI content and crystallization temperature on crystal nucleation, spherulite growth rate and crystallinity of α- and β-TPI crystals with X-ray diffraction (XRD) and polarized optical microscopy (POM) methods. The results showed that the incorporation of amorphous CPI caused a more severer suppression effect on the formation of α-TPI crystal than that on the formation of β-TPI crystal. A high crystallization temperature was beneficial to the formation of α-TPI, and a low temperature promoted the formation of β-TPI in CPI/TPI blends. These facts were rationalized by the different response of α-TPI and β-TPI crystals on the changed thermodynamic and kinetics of crystallization owing from the interaction between both isomers of CPI and TPI.