The local chain motion of syndiotactic and isotactic poly(methyl methacrylatejs (s-PMMA and i-PMMA) was examined by the time-resolved fluorescence depolarization method. The reduced relaxation time, Tm/p, and its activation energy, E*, were measured in various solvents. Both the TJr¡ and E* for s-and ¿-PMMAs decreased with a decrease in the local segment density. As for the effect of the stereoregularity, the activation energy of both PMMAs showed similar values, but the relaxation time of s-PMMA was ca. 1.5-2.0 times larger than that of ¿-PMMA. Such a difference in relaxation time is closely related to the static chain stiffness predicted by the helical wormlike (HW) chain model.