Urban parks and gardens green waste constitute a low-cost and highly available lignocellulosic-rich resource, that is currently treated in composting or anaerobic digestion processes. The present work investigated for the first time the potential of using urban green waste as raw resource for the production of lignocellulosic fillers by dry fractionation (combination of sorting and grinding processes). Five fractions of lignocellulosic fillers with controlled composition were produced: a branches-rich fraction, a grasses-rich fraction, a leaves-rich fraction, and two fractions constituted of a mixture of constituents. All the fractions were ground to reach an average median diameter around 100 µm. The reinforcing effect of each fraction was investigated and compared to that of the sample as a whole. Biocomposites based on a poly(3-hydroxybutyrate-co-3-hydroxyvalerate) as matrix were produced by melt extrusion, with filler contents up to 30 wt%. It was shown that the branches-rich fraction displayed the best reinforcing effect (e.g. stress at break of 37 ± 1 MPa for a filler content of 15 wt%, similar to that of the neat matrix) whereas the grasses-rich fraction slightly degraded the overall mechanical performance (e.g. stress at break of 33.5 ± 1.5 MPa for a filler content of 15 wt%). The dry fractionation and formulation steps could be thus adapted depending on the targeted application, e.g. by choosing to use the whole urban green waste resource, or to remove grasses, or to keep only branches.