Short rotation forestry (SRF) is a promising feedstock for biofuel production via thermochemical processes. This feedstock is highly heterogeneous, that could be problematic in case of segregation of ground samples. In order to assess an eventual segregation impact on biomass properties and potential consequences on thermochemical processes, 4 French poplar SRF sawdust feedstocks were sieved to particle size fractions (<0.2mm / 0.2mm-0.4mm / >0.4mm). Important properties (in regard to thermochemical processes) were measured on those fractions: lignocellulosic composition, ash content, and elemental composition of organic and inorganic fractions. Significant differences between particle size fractions could be observed on lignocellulosic composition, ash content and inorganic composition. Cellulose content increased with particle size while lignin content was higher in small particles. Ash content was ranging 1-4%w in the biggest particles and 7-10%w in the smallest ones. Important differences could also be observed on major inorganic elements such as Ca and K, which are known to impact the gasification processes. This study shows that segregation may have significant impact on SRF chemical properties. The differences found on lignocellulosic composition, ash content and inorganic composition seemed high enough to have an effect on biomass conversion in thermochemical processes. Therefore, attention must be paid in sampling SRF biomass for analytical purposes, and in process control. According to the observations carried out, the smallest particles of ground SRF could be removed from biomass feedstock to adjust some biomass thermochemical behavior. This fraction could then be used for other applications such as return to soil or green chemistry.