The local chain motion of syndiotactic and isotactic poly(methyl methacrylate)s (s-PMMA and i-PMMA) was examined by the time-resolved fluorescence depolarization method. The reduced relaxation time, T-m/eta, and its activation energy, E*, were measured in various solvents. Both the T-m/eta and E* for s- and i-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 i-PRIMA. Such a difference in relaxation time is closely related to the static chain stiffness predicted by the helical wormlike (HW) chain model.