The crystallization behaviour of syndiotactic polystyrene (sPS) and benzoylated sPS (BzsPS) was investigated by POM, DSC and XRD. The results suggest beta form of sPS has higher equilibrium melting temperature T-m(0) and the fold surface free energy sigma(e) than T-m(0) form. With increasing benzoylation degree the growth rates T-m(0) and T-m(0) of two forms decrease, but their T-m(0) decrement is very close; the sigma(e) of beta form more increases than that of alpha form, the formation of alpha is more favourable. Upon loading trace amount of alpha nucleating agent PTBBNa in samples the growth rate of two forms can be strictly compared in the same melting and crystallization temperature condition, the results reveal that the growth rate of beta form is faster than that of alpha form in sPS and BzsPS-2%. Using supercooling degree Delta T and sigma(e) two parameters has explained the formation competition mechanism of alpha and beta forms. (C) 2016 Elsevier Ltd. All rights reserved.