The molecular dynamics of Poly(L-lactic Acid) (PLLA) chains in the alpha phase was investigated by Solid-State NMR spectroscopy. C-13 high-resolution NMR clearly indicates that the crystalline signals split into 2, 3, and 4 signals for the CH3, CH and CO groups, respectively at 25 degrees C, while the amorphous signals give a broad component at the bottom of the crystalline signals. C-13 NMR spectra show that the crystalline line shape changes with increasing temperatures well above the glass transition temperature ( T-g) and imply the presence of the molecular dynamics in the crystalline region. Comparisons of the evolution-time dependence of CODEX data and simulation results based on reorientation of chemical shift anisotropy (CSA) indicate that the chains in the alpha phase perform helical jump motions in the slow dynamic range at temperatures above 115 degrees C. The mixing-time dependence of the CODEX data yields an activation energy of E-a of (95 +/- 8) kJ/mol for the helical jump motions. Moreover, two-dimensional exchange NMR with highly resolved signals for the CO group provides cross peaks among four well resolved signals due to the helical jumps. Comparison of 2D buildup curves of the cross peaks and calculated data determines that helical jump motions prefer largely uncorrelated random back,and-forth motions between the neighboring sites, possibly enabling large-scale chain diffusion in the crystalline regions.