This study explores the effect of cooling rates on order parameter of phase transitions of octylcyanobiphenyl (8CB) liquid crystal applying Johnson-Mehl-Avrami (JMA) and Matusita & Sakka (MS) models. The sample of 8CB was first heated and then cooled with various cooling rates from 5 K/min to 20 K/min to see the effect of cooling rate on phase transitions of 8CB. The 8CB liquid crystal shows three phase transitions namely isotropic to nematic (I-N), nematic to smectic A (N-SmA) and smectic A to crystalline (SmA-K) on cooling at 312.2 K, 305.3 K and 267 K, respectively. The appearance of transition peaks follows the transition behavior discussed and given by JMA theory and Ozawa model. JMA theory was then used to find the activation energy of each transition on cooling. Further, the MS model was used to find the order parameter (n) of each transition of 8CB on cooling when molecules of 8CB tends to move from completely disordered state to completely ordered state from isotropic phase to crystalline phase. The order parameter (n) of all phase transitions was found in the range of 0.30 to 0.82 for I-N to SmA-K phase transition and the activation energy (ΔEc) of the transitions was found in the range of 0.30 to 60 kJ/mol. The effect of cooling rates brings significant effect on order parameter “n” and activation energy “ΔEc” of phase transitions of 8CB, which shows the importance of phase transitions of 8CB liquid crystal applying JMA and MS models.