The thermal and dynamic mechanical properties of miscanthus stem fragments and differences between genotypes and positions along the stem are studied in relation with their biochemical and structural characteristics. The starting degradation temperature does not correlate to the biochemical composition. However, the first DTG peak temperature is negatively correlated to hemicelluloses content and positively correlated to lignin and p-coumaric contents. A pronounced genotypic effect is evidenced on fragments elastic moduli while limited effect of the position along the stem is found. This is mostly related to ferulic and p-coumaric acid contents of stem fragments for which a strong correlation to elastic moduli is evidenced. Our results highlight that genotypic effect, position along the stem, stem fragment dimensions and mechanical properties of miscanthus stem fragments are strongly interconnected in relation with their respective biochemical and structural characteristics. This opens interesting perspectives for identifying key biological traits that need to be optimized for a better selection of performing miscanthus genotypes targeted to polymer composite applications.