Quantization and abnormality of thermal conductance was discovered in low-dimensional nanostructures, where guided modes were proposed to contribute the universal quantum. However, no direct observation of the guided-mode propagation inside 1D nanostructures was thought possible, which is critical for quantitative transport-property studies. In this talk, we report direct observation of guided acoustic-phonon mode transportation inside semiconductor nanorods. The observed dispersion behavior agrees well with our theory. Moreover, owing to the dimensional discontinuousness, ≧ 50% acoustic wave reflection at the nanorod/substrate interface is found, which would play a crucial role in heat dissipation and thermal management in future nanodevices.