Isothermal crystallization of syndiotactic poly(propylene-co-olefin)s (olefin = ethylene, I-butene, I-pentene, l-hexene, 4-methyl-1-pentene) was studied. The melting behavior of isothermally crystallized polymers was investigated by differential scanning calorimetry, and the equilibrium melting temperature (T-m(0)) was determined by Hoffman-Week's plot. Crystallization rate and Avrami exponent of isothermally crystallized copolymers from the melt were measured by depolarized light intensity technique. The half time of crystallization (t(1/2)) was found to be dependent on the degree of supercooling (Delta T), but independent of the comonomer. The Avrami exponents (n) of copolymers were detected by the Avrami plot and the average n ranged from 2.0 to 2.8 for the primary crystallization process in any copolymer. The effect of isothermal crystallization temperature (T-c) on the crystalline structure of copolymers was studied by wide-angle X-ray diffraction (WAXD). The WAXD patterns of all the copolymers were similar to the pattern of Cell II in the syndiotactic polypropylene. The WAXD pattern of I-butene copolymer with small amount of I-butene indicated the existence of Cell III.