Over the last decade, the merits of sorghum as a dedicated feedstock have been highlighted. The relevance of sorghum biomass as an energy or biomaterial source relies on the possibility that its composition meets the requirement of the different production processes. In order to better assess the phenotypic variation existing in sorghum for stem composition, 103 accessions representing a broad genetic panel of insensitive and moderate photoperiod-sensitive landraces were evaluated during two consecutive years at Montpellier, South of France. Our data confirmed the existence of a great range of variation for several key parameters of stem composition, in particular for crude protein, lignin content and in vitro organic matter degradation and at a less extent for fibre digestibility. Sugar content in stems estimated by Brix was positively correlated with cycle duration and dry stem yield. Lignin content and fibre digestibility, two key traits linked to the potential utilization of sorghum biomass for fodder and 2nd-generation energy source, were strongly (positive and negative, respectively) correlated with plant height but not linked with dry stem yield. These results indicated that both biomass yield and quality can be improved simultaneously. Variability of stem composition was highly structured according to the genetic origins of the accessions. Durra and kafir groups emerged as good sources of high fibre digestibility. The same two groups and the photoperiod-insensitive caudatum from Africa comprised the best accessions for high sugar content in stems. Several Chinese caudatum and bicolor-caudatum accessions included in this panel stand out for high lignin content. This information will be mobilized to broaden the genetic diversity relevant for on-going breeding programs of sweet and biomass sorghum for temperate areas.